/* Neo4j EDU — design system
   Tokens and layout from DESIGN.md
   Colors: graphite-950/850, slate-650, cyan-400, amber-400, paper-100 only */

:root {
  --graphite-950: #0b0f12;
  --graphite-850: #12181d;
  --slate-650: #29343c;
  --cyan-400: #39d6e8;
  --amber-400: #e7a93b;
  --paper-100: #e8eef1;

  --text-secondary: rgba(232, 238, 241, 0.75);
  --text-muted: rgba(232, 238, 241, 0.61);
  --grid-line: rgba(41, 52, 60, 0.22);
  --hover-fill: rgba(57, 214, 232, 0.1);
  --inset-highlight: rgba(232, 238, 241, 0.04);
  --header-bg: rgba(11, 15, 18, 0.94);

  --font-display: "Barlow Condensed", "Arial Narrow", "Roboto Condensed", Arial, sans-serif;
  --font-body: "IBM Plex Sans", Inter, "Segoe UI", Arial, sans-serif;
  --font-mono: "IBM Plex Mono", "SFMono-Regular", Consolas, "Liberation Mono", monospace;

  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;
  --space-20: 80px;
  --space-24: 96px;
  --space-32: 128px;

  --radius-sm: 2px;
  --radius-md: 4px;
  --content-max: 1180px;
  --header-h: 72px;
  --control-h: 48px;
  --gutter: 32px;

  --display-1: clamp(2.875rem, 4vw + 1.5rem, 4.5rem);
  --display-2: clamp(2.25rem, 2.5vw + 1rem, 3rem);
  --heading-1: clamp(1.875rem, 1.5vw + 1rem, 2.375rem);
  --heading-2: clamp(1.625rem, 1vw + 1rem, 1.875rem);
  --heading-3: clamp(1.3125rem, 0.4vw + 1.1rem, 1.375rem);
  --body-lg: clamp(1.0625rem, 0.2vw + 1rem, 1.125rem);
  --body: 1rem;
  --label: 0.875rem;
  --micro: 0.75rem;

  --focus-ring: 0 0 0 2px var(--graphite-950), 0 0 0 4px var(--cyan-400);
  --transition-fast: 120ms ease;
  --transition-route: 160ms ease;
  --transition-draw: 800ms ease-out;
}

/* ——— Reset / base ——— */
*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .hero-graph .edge-path,
  .hero-graph .route-path {
    stroke-dasharray: none !important;
    stroke-dashoffset: 0 !important;
    animation: none !important;
  }
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: var(--font-body);
  font-size: var(--body);
  line-height: 1.6;
  color: var(--paper-100);
  background-color: var(--graphite-950);
  background-image:
    linear-gradient(var(--grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid-line) 1px, transparent 1px),
    linear-gradient(rgba(41, 52, 60, 0.12) 1px, transparent 1px),
    linear-gradient(90deg, rgba(41, 52, 60, 0.12) 1px, transparent 1px);
  background-size: 24px 24px, 24px 24px, 96px 96px, 96px 96px;
  background-position: 0 0, 0 0, 0 0, 0 0;
  overflow-x: hidden;
}

img,
svg {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--cyan-400);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.2em;
}

a:hover {
  text-decoration-thickness: 2px;
}

a:focus-visible,
button:focus-visible,
summary:focus-visible,
.lesson-card:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

:focus:not(:focus-visible) {
  outline: none;
  box-shadow: none;
}

button {
  font-family: inherit;
  cursor: pointer;
  border: none;
  background: none;
  color: inherit;
  padding: 0;
}

ul,
ol {
  margin: 0;
  padding: 0;
  list-style: none;
}

h1,
h2,
h3,
h4 {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.08;
}

p {
  margin: 0;
}

/* ——— Utilities ——— */
.container {
  width: 100%;
  max-width: var(--content-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.skip-link {
  position: absolute;
  top: -100px;
  left: var(--space-4);
  z-index: 1000;
  padding: var(--space-3) var(--space-5);
  background: var(--cyan-400);
  color: var(--graphite-950);
  font-family: var(--font-body);
  font-weight: 600;
  font-size: var(--label);
  text-decoration: none;
  border-radius: var(--radius-sm);
}

.skip-link:focus {
  top: var(--space-4);
  box-shadow: var(--focus-ring);
}

/* ——— Buttons ——— */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: var(--control-h);
  min-width: 44px;
  padding: 0 var(--space-6);
  font-family: var(--font-body);
  font-size: var(--label);
  font-weight: 600;
  line-height: 1.2;
  text-decoration: none;
  border-radius: var(--radius-sm);
  transition:
    background-color var(--transition-fast),
    color var(--transition-fast),
    box-shadow var(--transition-fast),
    transform var(--transition-fast);
}

.btn-primary {
  background-color: var(--cyan-400);
  color: var(--graphite-950);
  box-shadow: inset 0 -2px 0 rgba(11, 15, 18, 0.18);
}

.btn-primary:hover {
  background-color: #4fdeec;
  text-decoration: none;
  box-shadow: inset 0 -1px 0 rgba(11, 15, 18, 0.18);
}

.btn-primary:active {
  transform: translateY(1px);
}

.btn-primary:focus-visible {
  box-shadow: var(--focus-ring);
}

.link-secondary {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 44px;
  font-size: var(--label);
  font-weight: 500;
  color: var(--cyan-400);
  text-decoration: underline;
  text-underline-offset: 0.22em;
}

.link-secondary::after {
  content: "";
  display: inline-block;
  width: 14px;
  height: 1.5px;
  background: currentColor;
  position: relative;
  flex-shrink: 0;
}

.link-secondary::before {
  content: "";
  /* relationship terminal via after + diamond */
}

.link-secondary:hover {
  text-decoration-thickness: 2px;
}

/* ——— Header / Nav ——— */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-h);
  background: var(--header-bg);
  border-bottom: 1px solid var(--slate-650);
  backdrop-filter: blur(8px);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  gap: var(--space-4);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: var(--space-3);
  min-height: 44px;
  color: var(--paper-100);
  text-decoration: none;
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.25rem;
  letter-spacing: -0.02em;
}

.brand:hover {
  color: var(--paper-100);
  text-decoration: none;
}

.brand-mark {
  width: 28px;
  height: 28px;
  flex-shrink: 0;
}

.brand-mark .node {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.brand-mark .edge {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
  stroke-linecap: round;
}

.brand-mark .node-core {
  fill: var(--amber-400);
  stroke: none;
}

.brand-text span {
  color: var(--text-muted);
  font-weight: 600;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-2);
  min-height: 44px;
  min-width: 44px;
  padding: var(--space-2) var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 500;
  color: var(--paper-100);
  border: 1px solid transparent;
  border-radius: var(--radius-sm);
}

.nav-toggle:hover {
  background: var(--hover-fill);
}

.nav-toggle:focus-visible {
  box-shadow: var(--focus-ring);
}

.nav-toggle-icon {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 4px;
  width: 20px;
  height: 16px;
}

.nav-toggle-icon span {
  display: block;
  height: 1.5px;
  width: 100%;
  background: var(--cyan-400);
  border-radius: 1px;
}

.site-nav {
  display: flex;
  align-items: center;
}

.nav-list {
  display: flex;
  align-items: center;
  gap: var(--space-1);
}

.nav-list > li {
  position: relative;
}

.nav-link {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  padding: var(--space-2) var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  border-bottom: 2px solid transparent;
  transition:
    color var(--transition-fast),
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.nav-link:hover {
  color: var(--paper-100);
  background: var(--hover-fill);
  text-decoration: none;
}

.nav-link[aria-current="page"],
.nav-link.is-active {
  color: var(--paper-100);
  border-bottom-color: var(--cyan-400);
}

.nav-link:focus-visible {
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

/* Lessons dropdown */
.nav-dropdown {
  position: relative;
}

.nav-dropdown-trigger {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 44px;
  padding: var(--space-2) var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 500;
  color: var(--text-secondary);
  border-bottom: 2px solid transparent;
  border-radius: 0;
  transition:
    color var(--transition-fast),
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.nav-dropdown-trigger:hover,
.nav-dropdown-trigger[aria-expanded="true"] {
  color: var(--paper-100);
  background: var(--hover-fill);
}

.nav-dropdown-trigger:focus-visible {
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.nav-dropdown-trigger .chevron {
  width: 10px;
  height: 10px;
  border-right: 1.5px solid currentColor;
  border-bottom: 1.5px solid currentColor;
  transform: rotate(45deg) translateY(-2px);
  transition: transform var(--transition-fast);
}

.nav-dropdown-trigger[aria-expanded="true"] .chevron {
  transform: rotate(225deg) translateY(-1px);
}

.nav-lessons-details {
  position: relative;
}

.nav-lessons-details > summary {
  list-style: none;
  cursor: pointer;
}

.nav-lessons-details > summary::-webkit-details-marker {
  display: none;
}

.nav-lessons-details > summary::marker {
  content: "";
  display: none;
}

.nav-dropdown-panel {
  position: absolute;
  top: calc(100% + 4px);
  right: 0;
  min-width: 320px;
  max-width: min(380px, calc(100vw - 40px));
  max-height: min(70vh, 480px);
  overflow-y: auto;
  padding: var(--space-2) 0;
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: 0 12px 32px rgba(0, 0, 0, 0.35);
  z-index: 50;
}

/* Closed details hide panel; open details show it (no-JS resilient) */
.nav-lessons-details:not([open]) .nav-dropdown-panel {
  display: none;
}

.nav-lessons-details[open] .nav-dropdown-trigger,
.nav-dropdown-trigger[aria-expanded="true"] {
  color: var(--paper-100);
  background: var(--hover-fill);
}

.nav-lessons-details[open] .nav-dropdown-trigger .chevron {
  transform: rotate(225deg) translateY(-1px);
}

.nav-dropdown-panel a {
  display: flex;
  align-items: baseline;
  gap: var(--space-3);
  padding: var(--space-3) var(--space-5);
  font-family: var(--font-mono);
  font-size: var(--micro);
  color: var(--text-secondary);
  text-decoration: none;
  min-height: 44px;
  border-left: 2px solid transparent;
  transition:
    background-color var(--transition-fast),
    color var(--transition-fast),
    border-color var(--transition-fast);
}

.nav-dropdown-panel a:hover,
.nav-dropdown-panel a:focus-visible {
  background: var(--hover-fill);
  color: var(--paper-100);
  border-left-color: var(--cyan-400);
  text-decoration: none;
}

.nav-dropdown-panel a:focus-visible {
  box-shadow: none;
  outline: 2px solid var(--cyan-400);
  outline-offset: -2px;
}

.nav-dropdown-panel .lesson-num {
  color: var(--amber-400);
  font-weight: 600;
  flex-shrink: 0;
  min-width: 1.5em;
}

.nav-dropdown-panel .lesson-name {
  color: inherit;
  font-family: var(--font-body);
  font-size: var(--label);
  line-height: 1.35;
}

/* ——— Hero ——— */
.hero {
  position: relative;
  padding-block: var(--space-16) var(--space-12);
  min-height: clamp(auto, 100%, 860px);
}

.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 5fr) minmax(0, 7fr);
  gap: var(--space-10) var(--space-8);
  align-items: start;
}

.hero-copy {
  max-width: 28rem;
  padding-top: var(--space-6);
}

.hero-title {
  font-size: var(--display-1);
  line-height: 0.96;
  font-weight: 700;
  color: var(--paper-100);
  margin-bottom: var(--space-6);
}

.hero-lead {
  font-size: var(--body-lg);
  line-height: 1.55;
  color: var(--text-secondary);
  margin-bottom: var(--space-8);
  max-width: 36ch;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-5) var(--space-6);
}

.hero-visual {
  position: relative;
  min-height: 320px;
}

.hero-graph {
  width: 100%;
  max-width: 560px;
  margin-inline: auto;
  aspect-ratio: 5 / 4;
}

.hero-graph .edge-path {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.hero-graph .route-path {
  fill: none;
  stroke: var(--amber-400);
  stroke-width: 1.75;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.hero-graph .node-ring {
  fill: var(--graphite-950);
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.hero-graph .node-ring-active {
  fill: var(--graphite-850);
  stroke: var(--amber-400);
  stroke-width: 2;
}

.hero-graph .node-fill {
  fill: var(--amber-400);
}

.hero-graph .label {
  fill: var(--paper-100);
  font-family: var(--font-mono);
  font-size: 11px;
  text-anchor: middle;
}

.hero-graph .edge-label {
  fill: var(--cyan-400);
  font-family: var(--font-mono);
  font-size: 10px;
  text-anchor: middle;
}

.hero-graph .edge-label-route {
  fill: var(--amber-400);
}

.hero-graph .edge-path.draw,
.hero-graph .route-path.draw {
  stroke-dasharray: 400;
  stroke-dashoffset: 400;
  animation: draw-path var(--transition-draw) forwards;
}

.hero-graph .node-ring,
.hero-graph .node-ring-active {
  opacity: 0;
  animation: socket-settle 150ms ease-out 700ms forwards;
}

@keyframes draw-path {
  to {
    stroke-dashoffset: 0;
  }
}

@keyframes socket-settle {
  to {
    opacity: 1;
  }
}

.hero-code-wrap {
  grid-column: 1 / -1;
  display: flex;
  justify-content: center;
  margin-top: var(--space-2);
  position: relative;
}

.hero-code-wrap::before {
  content: "";
  position: absolute;
  top: -24px;
  left: 50%;
  width: 1.5px;
  height: 24px;
  background: var(--amber-400);
  transform: translateX(-50%);
}

/* ——— Code panel ——— */
.code-panel {
  width: 100%;
  max-width: 560px;
  background: var(--graphite-950);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.code-panel-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 36px;
  padding: 0 var(--space-4);
  background: var(--graphite-850);
  border-bottom: 1px solid var(--slate-650);
}

.code-lang {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.06em;
  color: var(--cyan-400);
  text-transform: uppercase;
}

.code-copy {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  color: var(--text-muted);
  border-radius: var(--radius-sm);
  transition: color var(--transition-fast), background-color var(--transition-fast);
}

.code-copy:hover {
  color: var(--cyan-400);
  background: var(--hover-fill);
}

.code-copy:focus-visible {
  box-shadow: var(--focus-ring);
}

.code-panel pre {
  margin: 0;
  padding: var(--space-5) var(--space-5);
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.875rem;
  line-height: 1.55;
  color: var(--paper-100);
  background: transparent;
}

.code-panel code {
  font-family: inherit;
  font-size: inherit;
  white-space: pre;
}

.tok-kw {
  color: var(--cyan-400);
  font-weight: 500;
}

.tok-rel {
  color: var(--amber-400);
}

.tok-plain {
  color: var(--paper-100);
}

/* ——— Course abstract ——— */
.course-abstract {
  padding-block: var(--space-12) var(--space-16);
}

.abstract-panel {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: var(--space-6) var(--space-8);
  align-items: center;
  padding: var(--space-8) var(--space-10);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
  position: relative;
}

.abstract-diagram {
  width: 72px;
  height: 72px;
  flex-shrink: 0;
}

.abstract-diagram .edge {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.abstract-diagram .node {
  fill: var(--graphite-850);
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.abstract-title {
  font-size: var(--heading-3);
  margin-bottom: var(--space-3);
  color: var(--paper-100);
}

.abstract-body {
  font-size: var(--body);
  line-height: 1.55;
  color: var(--text-secondary);
  max-width: 52ch;
}

/* ——— Curriculum / Course Route ——— */
.curriculum {
  padding-block: 0 var(--space-20);
  position: relative;
}

.curriculum-heading {
  font-size: var(--heading-2);
  margin-bottom: var(--space-16);
  color: var(--paper-100);
}

.course-route {
  position: relative;
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
}

/* Central vertical rail */
.course-route::before {
  content: "";
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  width: 1.5px;
  background: linear-gradient(
    to bottom,
    var(--amber-400) 0%,
    var(--amber-400) 85%,
    var(--cyan-400) 100%
  );
  transform: translateX(-50%);
  z-index: 0;
  pointer-events: none;
}

.lesson-row {
  position: relative;
  display: grid;
  grid-template-columns: 1fr 48px 1fr;
  gap: var(--space-4);
  align-items: center;
  z-index: 1;
}

.lesson-row--left .lesson-card-slot {
  grid-column: 1;
  justify-self: end;
  width: 100%;
  max-width: 480px;
}

.lesson-row--left .route-socket {
  grid-column: 2;
}

.lesson-row--left .lesson-spacer {
  grid-column: 3;
}

.lesson-row--right .lesson-spacer {
  grid-column: 1;
}

.lesson-row--right .route-socket {
  grid-column: 2;
}

.lesson-row--right .lesson-card-slot {
  grid-column: 3;
  justify-self: start;
  width: 100%;
  max-width: 480px;
}

.route-socket {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 48px;
  height: 48px;
  position: relative;
  z-index: 2;
}

.route-socket-inner {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: 50%;
  border: 2px solid var(--amber-400);
  background: var(--graphite-950);
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  color: var(--amber-400);
  line-height: 1;
}

/* Connector from socket to card */
.lesson-row--left .lesson-card-slot::after,
.lesson-row--right .lesson-card-slot::before {
  content: "";
  position: absolute;
  top: 50%;
  width: 0;
  height: 1.5px;
  background: var(--cyan-400);
  transition: width var(--transition-route);
  pointer-events: none;
}

.lesson-row--left .lesson-card-slot {
  position: relative;
}

.lesson-row--left .lesson-card-slot::after {
  right: -16px;
  transform: translateY(-50%);
}

.lesson-row--right .lesson-card-slot {
  position: relative;
}

.lesson-row--right .lesson-card-slot::before {
  left: -16px;
  transform: translateY(-50%);
}

.lesson-row:hover .lesson-card-slot::after,
.lesson-row:hover .lesson-card-slot::before,
.lesson-row:focus-within .lesson-card-slot::after,
.lesson-row:focus-within .lesson-card-slot::before {
  width: 16px;
}

.lesson-card {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: var(--space-4) var(--space-5);
  align-items: start;
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: inherit;
  box-shadow: inset 0 1px 0 var(--inset-highlight);
  transition:
    border-color var(--transition-fast),
    background-color var(--transition-fast);
  min-height: 96px;
}

.lesson-card:hover,
.lesson-card:focus-visible {
  border-color: var(--cyan-400);
  background: rgba(18, 24, 29, 0.95);
  text-decoration: none;
  color: inherit;
}

.lesson-thumb {
  width: 96px;
  height: 72px;
  flex-shrink: 0;
  background: var(--graphite-950);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

.lesson-thumb svg {
  width: 100%;
  height: 100%;
}

.lesson-thumb .edge {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.lesson-thumb .node {
  fill: var(--graphite-950);
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.lesson-thumb .accent {
  fill: none;
  stroke: var(--amber-400);
  stroke-width: 1.5;
}

.lesson-body {
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  padding-top: 2px;
}

.lesson-title {
  font-family: var(--font-display);
  font-size: 1.125rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.2;
  color: var(--paper-100);
}

.lesson-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-2) var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--micro);
  color: var(--text-muted);
}

.lesson-meta .sep {
  display: inline-block;
  width: 4px;
  height: 4px;
  background: var(--amber-400);
  flex-shrink: 0;
}

/* ——— Exam CTA ——— */
.exam-cta {
  padding-block: 0 var(--space-24);
}

.exam-slab {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: var(--space-6) var(--space-8);
  align-items: center;
  padding: var(--space-8) var(--space-10);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exam-icon {
  width: 56px;
  height: 56px;
  color: var(--cyan-400);
}

.exam-icon svg {
  width: 100%;
  height: 100%;
}

.exam-copy h2 {
  font-size: var(--heading-2);
  margin-bottom: var(--space-3);
  color: var(--paper-100);
}

.exam-copy p {
  font-size: var(--body);
  color: var(--text-secondary);
  max-width: 40ch;
}

.exam-slab .btn {
  white-space: nowrap;
}

/* ——— Footer ——— */
.site-footer {
  border-top: 1px solid var(--slate-650);
  background: var(--graphite-950);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  min-height: 120px;
  align-items: center;
}

.footer-cell {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--space-6) var(--space-4);
  min-height: 72px;
  text-align: center;
}

.footer-cell:not(:last-child) {
  border-right: 1px solid var(--slate-650);
}

.footer-brand {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.125rem;
  color: var(--paper-100);
  text-decoration: none;
  letter-spacing: -0.02em;
}

.footer-brand:hover {
  color: var(--cyan-400);
  text-decoration: none;
}

.footer-credit {
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--text-secondary);
}

.footer-credit a {
  color: var(--cyan-400);
  text-decoration: underline;
  text-underline-offset: 0.2em;
}

.footer-credit a:hover {
  text-decoration-thickness: 2px;
}

.footer-site a {
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--cyan-400);
}

/* ——— 404 page ——— */
.page-404 {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.page-404 main {
  flex: 1;
  display: flex;
  align-items: center;
  padding-block: var(--space-20);
}

.error-panel {
  max-width: 520px;
  margin-inline: auto;
  text-align: center;
  padding: var(--space-10);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
}

.error-code {
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 600;
  color: var(--amber-400);
  letter-spacing: 0.08em;
  margin-bottom: var(--space-4);
}

.error-panel h1 {
  font-size: var(--heading-1);
  margin-bottom: var(--space-4);
}

.error-panel p {
  color: var(--text-secondary);
  margin-bottom: var(--space-8);
}

.error-graph {
  width: 120px;
  height: 80px;
  margin: 0 auto var(--space-8);
}

.error-graph .edge {
  fill: none;
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.error-graph .node {
  fill: var(--graphite-850);
  stroke: var(--cyan-400);
  stroke-width: 1.5;
}

.error-graph .missing {
  stroke: var(--amber-400);
  stroke-dasharray: 4 3;
}

/* ——— Responsive ——— */
@media (max-width: 1199px) {
  :root {
    --gutter: 24px;
    --header-h: 72px;
  }

  .hero-grid {
    grid-template-columns: 1fr 1fr;
    gap: var(--space-8);
  }

  .abstract-panel {
    padding: var(--space-6) var(--space-8);
  }

  .lesson-card {
    padding: var(--space-4) var(--space-5);
  }
}

@media (max-width: 767px) {
  :root {
    --gutter: 20px;
    --header-h: 64px;
    --control-h: 52px;
  }

  .nav-toggle {
    display: inline-flex;
  }

  .site-nav {
    position: fixed;
    inset: var(--header-h) 0 auto 0;
    background: var(--graphite-850);
    border-bottom: 1px solid var(--slate-650);
    max-height: 0;
    overflow: hidden;
    opacity: 0;
    visibility: hidden;
    transition:
      max-height 200ms ease,
      opacity var(--transition-fast),
      visibility var(--transition-fast);
    z-index: 99;
  }

  .site-nav.is-open {
    max-height: min(85vh, 640px);
    overflow-y: auto;
    opacity: 1;
    visibility: visible;
  }

  /* No-JS: expose primary links in a document flow sheet */
  html.no-js .site-header {
    height: auto;
    min-height: var(--header-h);
  }

  html.no-js .site-header .container {
    flex-wrap: wrap;
    height: auto;
    min-height: var(--header-h);
    padding-block: var(--space-2);
  }

  html.no-js .nav-toggle {
    display: none;
  }

  html.no-js .site-nav {
    position: static;
    max-height: none;
    overflow: visible;
    opacity: 1;
    visibility: visible;
    width: 100%;
    border-top: 1px solid var(--slate-650);
    margin-top: var(--space-2);
  }

  .nav-list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: 0;
  }

  .nav-list > li {
    border-bottom: 1px solid var(--slate-650);
  }

  .nav-list > li:last-child {
    border-bottom: none;
  }

  .nav-link,
  .nav-dropdown-trigger {
    width: 100%;
    justify-content: flex-start;
    min-height: 52px;
    padding: var(--space-4) var(--space-5);
    border-bottom: none;
    border-left: 2px solid transparent;
  }

  .nav-link[aria-current="page"],
  .nav-link.is-active {
    border-bottom: none;
    border-left-color: var(--cyan-400);
    background: var(--hover-fill);
  }

  .nav-dropdown-panel {
    position: static;
    min-width: 0;
    max-width: none;
    max-height: none;
    border: none;
    border-radius: 0;
    box-shadow: none;
    background: var(--graphite-950);
  }

  .nav-lessons-details:not([open]) .nav-dropdown-panel {
    display: none;
  }

  .nav-dropdown-panel a {
    padding-left: var(--space-8);
  }

  .hero {
    padding-block: var(--space-10) var(--space-8);
  }

  .hero-grid {
    grid-template-columns: 1fr;
    gap: var(--space-8);
  }

  .hero-copy {
    max-width: none;
    padding-top: 0;
  }

  .hero-lead {
    max-width: none;
  }

  .hero-actions {
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-4);
  }

  .hero-actions .btn-primary {
    width: 100%;
  }

  .hero-actions .link-secondary {
    align-self: flex-start;
  }

  .hero-visual {
    min-height: 0;
  }

  .hero-graph {
    max-width: 100%;
    aspect-ratio: 16 / 10;
  }

  .hero-code-wrap {
    margin-top: var(--space-2);
  }

  .hero-code-wrap::before {
    display: none;
  }

  .code-panel {
    max-width: none;
  }

  .course-abstract {
    padding-block: var(--space-10) var(--space-12);
  }

  .abstract-panel {
    grid-template-columns: 1fr;
    gap: var(--space-5);
    padding: var(--space-5) var(--space-6);
  }

  .abstract-diagram {
    width: 56px;
    height: 56px;
  }

  .curriculum-heading {
    margin-bottom: var(--space-10);
  }

  .course-route {
    gap: var(--space-4);
    padding-left: var(--space-2);
  }

  .course-route::before {
    left: 18px;
    transform: none;
  }

  .lesson-row,
  .lesson-row--left,
  .lesson-row--right {
    display: grid;
    grid-template-columns: 36px 1fr;
    gap: var(--space-3) var(--space-4);
  }

  .lesson-row--left .route-socket,
  .lesson-row--right .route-socket {
    grid-column: 1;
    grid-row: 1;
    width: 36px;
    height: 36px;
  }

  .route-socket-inner {
    width: 32px;
    height: 32px;
    font-size: 11px;
  }

  .lesson-row--left .lesson-card-slot,
  .lesson-row--right .lesson-card-slot {
    grid-column: 2;
    grid-row: 1;
    max-width: none;
    justify-self: stretch;
  }

  .lesson-spacer {
    display: none;
  }

  .lesson-row--left .lesson-card-slot::after,
  .lesson-row--right .lesson-card-slot::before {
    display: none;
  }

  .lesson-card {
    grid-template-columns: auto 1fr;
    padding: var(--space-4);
    gap: var(--space-3) var(--space-4);
  }

  .lesson-thumb {
    width: 72px;
    height: 56px;
  }

  .lesson-title {
    font-size: 1.05rem;
  }

  .exam-cta {
    padding-block: 0 var(--space-16);
  }

  .exam-slab {
    grid-template-columns: 1fr;
    gap: var(--space-5);
    padding: var(--space-6);
    text-align: left;
  }

  .exam-slab .btn {
    width: 100%;
  }

  .footer-grid {
    grid-template-columns: 1fr;
    min-height: 0;
  }

  .footer-cell {
    border-right: none !important;
    border-bottom: 1px solid var(--slate-650);
    min-height: 56px;
    padding: var(--space-5);
  }

  .footer-cell:last-child {
    border-bottom: none;
  }
}

@media (max-width: 419px) {
  .lesson-thumb {
    width: 64px;
    height: 52px;
  }

  .lesson-meta {
    gap: var(--space-2);
  }

  .nav-dropdown-panel a {
    padding-left: var(--space-6);
  }

  .hero-title {
    font-size: 2.75rem;
  }
}

/* Body lock when mobile menu open */
body.nav-open {
  overflow: hidden;
}

/* Screen-reader only */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ==========================================================================
   Lesson pages — graph-blueprint components
   Contract: LESSON_AUTHORING.md
   Append-only; does not regress homepage/404 styles above.
   ========================================================================== */

/* ——— Page shell / reading layout ——— */
.lesson-page {
  padding-block: var(--space-8) var(--space-20);
}

.lesson-page > .container,
.lesson-page .lesson-inner {
  width: 100%;
  max-width: var(--content-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

/* Allow authors to put .container on sections or wrap once */
.lesson-page > section,
.lesson-page > header,
.lesson-page > nav {
  width: 100%;
  max-width: var(--content-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.lesson-page > section + section,
.lesson-page > header + section,
.lesson-page > section + nav,
.lesson-page > nav + section {
  margin-top: var(--space-16);
}

.reading-column {
  max-width: 720px;
}

.reading-column > p + p {
  margin-top: var(--space-4);
}

.reading-column > p {
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.6;
}

.section-heading {
  font-family: var(--font-display);
  font-size: var(--heading-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.12;
  color: var(--paper-100);
  margin-bottom: var(--space-4);
}

.section-lead {
  max-width: 720px;
  color: var(--text-secondary);
  font-size: var(--body-lg);
  line-height: 1.55;
  margin-bottom: var(--space-6);
}

/* ——— Breadcrumb ——— */
.lesson-breadcrumb {
  margin-bottom: var(--space-6);
}

.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-2);
  list-style: none;
  margin: 0;
  padding: 0;
  font-family: var(--font-mono);
  font-size: var(--micro);
  line-height: 1.35;
  color: var(--text-muted);
}

.breadcrumb-list li {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
}

.breadcrumb-list li:not(:last-child)::after {
  content: "/";
  color: var(--slate-650);
  margin-left: var(--space-2);
  speak: never;
}

.breadcrumb-list a {
  color: var(--cyan-400);
  text-decoration: none;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
}

.breadcrumb-list a:hover {
  text-decoration: underline;
  text-underline-offset: 0.2em;
}

.breadcrumb-list a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.breadcrumb-current {
  color: var(--paper-100);
  font-weight: 500;
}

/* ——— Masthead ——— */
.lesson-masthead {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: var(--space-5) var(--space-6);
  align-items: start;
  padding: var(--space-8);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
  margin-bottom: var(--space-12);
}

.masthead-socket {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 56px;
  height: 56px;
  border: 1.5px solid var(--cyan-400);
  border-radius: 50%;
  background: var(--graphite-950);
  box-shadow: inset 0 0 0 4px var(--graphite-850);
  flex-shrink: 0;
}

.masthead-num {
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 600;
  letter-spacing: 0.04em;
  color: var(--cyan-400);
  line-height: 1;
}

.masthead-body {
  min-width: 0;
}

.masthead-kicker {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--amber-400);
  margin-bottom: var(--space-2);
}

.masthead-title {
  font-family: var(--font-display);
  font-size: var(--heading-1);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.08;
  color: var(--paper-100);
  margin-bottom: var(--space-4);
}

.masthead-meta {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-4);
  font-family: var(--font-mono);
  font-size: var(--label);
  line-height: 1.35;
  color: var(--text-muted);
}

.meta-label {
  display: block;
  font-size: var(--micro);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: 2px;
}

.meta-value,
.masthead-meta time {
  color: var(--paper-100);
  font-weight: 500;
}

.meta-sep {
  display: inline-block;
  width: 4px;
  height: 4px;
  background: var(--amber-400);
  flex-shrink: 0;
  align-self: center;
}

/* ——— Objectives ——— */
.lesson-objectives {
  padding-bottom: var(--space-4);
}

.objectives-list {
  max-width: 720px;
  margin: 0;
  padding: 0;
  list-style: none;
  counter-reset: objective;
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.objectives-list > li {
  counter-increment: objective;
  display: grid;
  grid-template-columns: 36px 1fr;
  gap: var(--space-3);
  align-items: start;
  padding: var(--space-4) var(--space-5);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.55;
}

.objectives-list > li::before {
  content: counter(objective, decimal-leading-zero);
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  color: var(--cyan-400);
  line-height: 1.6;
  padding-top: 2px;
}

/* ——— Theory ——— */
.lesson-theory {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.theory-block {
  margin-top: var(--space-10);
}

.theory-block:first-of-type {
  margin-top: var(--space-6);
}

.theory-title {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  color: var(--paper-100);
  margin-bottom: var(--space-4);
  padding-left: var(--space-4);
  border-left: 2px solid var(--cyan-400);
}

.theory-block .code-panel,
.theory-block .syntax-block,
.theory-block .lesson-diagram,
.theory-block .table-scroll {
  margin-top: var(--space-6);
  max-width: 100%;
}

/* Definition square — key term callout (lesson theory) */
.definition-square {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: var(--space-3);
  width: min(100%, 320px);
  aspect-ratio: 1 / 1;
  margin: var(--space-6) 0;
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  box-shadow:
    inset 0 1px 0 var(--inset-highlight),
    inset 0 0 0 1px rgba(57, 214, 232, 0.08);
  position: relative;
}

.definition-square::before {
  content: "";
  position: absolute;
  inset: 6px;
  border: 1px solid rgba(57, 214, 232, 0.22);
  border-radius: 1px;
  pointer-events: none;
}

.definition-square-label {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--cyan-400);
}

.definition-square-term {
  margin: 0;
  font-family: var(--font-display);
  font-size: var(--heading-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.05;
  color: var(--paper-100);
}

.definition-square-body {
  margin: 0;
  font-size: var(--label);
  line-height: 1.5;
  color: var(--text-secondary);
}

.definition-square-body .inline-code {
  font-size: 0.92em;
}

.reading-column > .definition-square {
  margin-left: 0;
  margin-right: auto;
}

@media (max-width: 480px) {
  .definition-square {
    width: 100%;
    aspect-ratio: auto;
    min-height: 0;
  }
}

/* Lesson pages: code panels may use full content width */
.lesson-page .code-panel {
  max-width: none;
}

.lesson-page .syntax-block {
  margin-block: var(--space-6);
}

/* Extra token classes for annotated syntax */
.tok-str {
  color: var(--amber-400);
}

.tok-num {
  color: var(--paper-100);
  font-weight: 500;
}

.tok-comment {
  color: var(--text-muted);
  font-style: italic;
}

.inline-code {
  font-family: var(--font-mono);
  font-size: 0.875em;
  color: var(--cyan-400);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  padding: 0.1em 0.35em;
  white-space: nowrap;
}

/* ——— Tables (result sets) ——— */
.table-scroll {
  width: 100%;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  background: var(--graphite-950);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.table-scroll:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

.result-table {
  width: 100%;
  min-width: 280px;
  border-collapse: collapse;
  font-family: var(--font-mono);
  font-size: var(--label);
  line-height: 1.4;
  color: var(--paper-100);
}

.result-table th,
.result-table td {
  padding: var(--space-3) var(--space-4);
  text-align: left;
  border-bottom: 1px solid var(--slate-650);
  white-space: nowrap;
}

.result-table th {
  background: var(--graphite-850);
  color: var(--cyan-400);
  font-weight: 600;
  font-size: var(--micro);
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.result-table tbody tr:last-child td {
  border-bottom: none;
}

.result-table tbody tr:nth-child(even) td {
  background: rgba(18, 24, 29, 0.55);
}

/* ——— Diagrams ——— */
.lesson-diagram {
  margin: var(--space-8) 0 0;
  padding: 0;
  max-width: 100%;
}

.lesson-diagram img {
  width: 100%;
  max-width: 720px;
  height: auto;
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  background: var(--graphite-850);
}

.diagram-caption {
  max-width: 720px;
  margin-top: var(--space-3);
  font-size: var(--label);
  line-height: 1.45;
  color: var(--text-muted);
}

/* ——— Example cards ——— */
.lesson-examples {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.example-card {
  margin-top: var(--space-8);
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.example-card + .example-card {
  margin-top: var(--space-8);
}

.example-header {
  display: flex;
  align-items: baseline;
  gap: var(--space-4);
  margin-bottom: var(--space-4);
  flex-wrap: wrap;
}

.example-num {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.06em;
  color: var(--amber-400);
  flex-shrink: 0;
}

.example-title {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  color: var(--paper-100);
}

.example-setup {
  margin-bottom: var(--space-5);
  color: var(--text-secondary);
}

.example-card .code-panel {
  margin-top: var(--space-4);
}

.example-result {
  margin-top: var(--space-6);
}

.example-result-label {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin-bottom: var(--space-3);
}

/* ——— Pitfalls ——— */
.lesson-pitfalls {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.pitfalls-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  max-width: 800px;
}

.pitfall-item {
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-left: 3px solid var(--amber-400);
  border-radius: var(--radius-sm);
}

.pitfall-title {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  color: var(--paper-100);
  margin-bottom: var(--space-2);
}

.pitfall-body {
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.6;
  margin: 0;
}

/* ——— Exercises ——— */
.lesson-exercises {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.exercises-list {
  list-style: none;
  margin: 0;
  padding: 0;
  counter-reset: exercise;
  display: flex;
  flex-direction: column;
  gap: var(--space-8);
}

.exercise-item {
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exercise-title {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
  color: var(--paper-100);
  margin-bottom: var(--space-3);
}

.exercise-num {
  font-family: var(--font-mono);
  font-size: 0.9em;
  font-weight: 600;
  color: var(--cyan-400);
  margin-right: var(--space-2);
}

.exercise-prompt {
  margin-bottom: var(--space-5);
  color: var(--text-secondary);
}

.exercise-starter {
  margin-top: var(--space-4);
}

.exercise-starter .code-lang {
  color: var(--amber-400);
}

/* ——— Video frame ——— */
.lesson-video {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.video-frame {
  position: relative;
  width: 100%;
  max-width: 800px;
  aspect-ratio: 16 / 9;
  background: var(--graphite-950);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  overflow: hidden;
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.video-frame iframe,
.video-frame video {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: 0;
}

.video-frame video {
  object-fit: contain;
  background: var(--graphite-950);
}

.video-fallback {
  max-width: 800px;
  margin-top: var(--space-4);
  font-size: var(--label);
  color: var(--text-muted);
  line-height: 1.45;
}

.video-fallback a {
  color: var(--cyan-400);
}

/* ——— Resources ——— */
.lesson-resources {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.resources-list {
  list-style: none;
  margin: 0;
  padding: 0;
  max-width: 720px;
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.resources-list > li {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-2);
  padding: var(--space-3) 0;
  border-bottom: 1px solid rgba(41, 52, 60, 0.65);
  font-size: var(--body);
  line-height: 1.5;
}

.resources-list > li:last-child {
  border-bottom: none;
}

.resources-list a {
  color: var(--cyan-400);
  font-weight: 500;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
}

.resources-list a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.resource-note {
  color: var(--text-muted);
  font-size: var(--label);
}

/* ——— Quiz ——— */
.lesson-quiz {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.quiz-mount {
  max-width: 720px;
  margin-top: var(--space-6);
}

.quiz-root {
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
}

.quiz-loading,
.quiz-status {
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--text-muted);
  margin: 0;
}

.quiz-error {
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-left: 3px solid var(--amber-400);
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.55;
}

.quiz-error[role="alert"] {
  color: var(--paper-100);
}

.quiz-form {
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
  margin: 0;
}

.quiz-question {
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.quiz-question.is-correct {
  border-color: var(--cyan-400);
}

.quiz-question.is-incorrect {
  border-color: var(--amber-400);
}

.quiz-q-meta {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  margin-bottom: var(--space-3);
}

.quiz-prompt {
  font-family: var(--font-body);
  font-size: var(--body);
  font-weight: 500;
  line-height: 1.5;
  color: var(--paper-100);
  margin: 0 0 var(--space-4);
}

.quiz-options {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.quiz-option {
  margin: 0;
}

.quiz-option label {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: var(--space-3);
  align-items: start;
  min-height: 48px;
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  background: var(--graphite-950);
  cursor: pointer;
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.45;
  transition:
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.quiz-option label:hover {
  background: var(--hover-fill);
  border-color: rgba(57, 214, 232, 0.35);
}

.quiz-option input[type="radio"] {
  width: 18px;
  height: 18px;
  margin: 2px 0 0;
  accent-color: var(--cyan-400);
  flex-shrink: 0;
  cursor: pointer;
}

.quiz-option input[type="radio"]:focus-visible + .quiz-option-text,
.quiz-option label:has(input[type="radio"]:focus-visible) {
  box-shadow: var(--focus-ring);
}

.quiz-option label:has(input[type="radio"]:checked) {
  border-color: var(--cyan-400);
  background: var(--hover-fill);
  color: var(--paper-100);
}

.quiz-option-text {
  min-width: 0;
}

.quiz-question.is-locked .quiz-option label {
  cursor: default;
}

.quiz-question.is-locked .quiz-option input[type="radio"] {
  cursor: default;
}

.quiz-feedback {
  margin-top: var(--space-4);
  padding: var(--space-3) var(--space-4);
  font-size: var(--label);
  line-height: 1.45;
  border-radius: var(--radius-sm);
  border: 1px solid var(--slate-650);
  background: var(--graphite-950);
  color: var(--text-secondary);
}

.quiz-feedback.is-correct {
  border-color: rgba(57, 214, 232, 0.45);
  color: var(--paper-100);
}

.quiz-feedback.is-incorrect {
  border-color: rgba(231, 169, 59, 0.55);
  color: var(--paper-100);
}

.quiz-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
  align-items: center;
}

.quiz-submit,
.quiz-reset {
  /* reuse .btn when present; standalone fallback */
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: var(--control-h);
  min-width: 44px;
  padding: 0 var(--space-6);
  font-family: var(--font-body);
  font-size: var(--label);
  font-weight: 600;
  line-height: 1.2;
  border-radius: var(--radius-sm);
  transition:
    background-color var(--transition-fast),
    color var(--transition-fast),
    box-shadow var(--transition-fast),
    transform var(--transition-fast);
}

.quiz-submit {
  background-color: var(--cyan-400);
  color: var(--graphite-950);
  box-shadow: inset 0 -2px 0 rgba(11, 15, 18, 0.18);
  border: none;
}

.quiz-submit:hover:not(:disabled) {
  background-color: #4fdeec;
  box-shadow: inset 0 -1px 0 rgba(11, 15, 18, 0.18);
}

.quiz-submit:active:not(:disabled) {
  transform: translateY(1px);
}

.quiz-submit:focus-visible,
.quiz-reset:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

.quiz-submit:disabled {
  opacity: 0.55;
  cursor: not-allowed;
  transform: none;
}

.quiz-reset {
  background: transparent;
  color: var(--cyan-400);
  border: 1px solid var(--slate-650);
  text-decoration: none;
}

.quiz-reset:hover {
  background: var(--hover-fill);
  border-color: var(--cyan-400);
}

/* Score */
.quiz-score {
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.quiz-score-value {
  font-family: var(--font-display);
  font-size: var(--heading-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--paper-100);
  margin: 0 0 var(--space-2);
}

.quiz-score-value .quiz-score-fraction {
  font-family: var(--font-mono);
  font-size: 0.85em;
  color: var(--cyan-400);
  font-weight: 600;
}

.quiz-score-summary {
  margin: 0;
  font-size: var(--body);
  color: var(--text-secondary);
  line-height: 1.55;
}

/* Answer key */
.quiz-answer-key {
  margin: 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.quiz-answer-key > .quiz-key-heading {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--paper-100);
  margin: 0;
  list-style: none;
}

.quiz-key-item {
  padding: var(--space-5);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
}

.quiz-key-item.quiz-key-correct {
  border-left: 3px solid var(--cyan-400);
}

.quiz-key-item.quiz-key-incorrect {
  border-left: 3px solid var(--amber-400);
}

.quiz-key-status {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  margin-bottom: var(--space-2);
}

.quiz-key-correct .quiz-key-status {
  color: var(--cyan-400);
}

.quiz-key-incorrect .quiz-key-status {
  color: var(--amber-400);
}

.quiz-key-prompt {
  font-weight: 500;
  color: var(--paper-100);
  margin: 0 0 var(--space-2);
  font-size: var(--body);
  line-height: 1.45;
}

.quiz-key-answer,
.quiz-key-yours {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--text-secondary);
  line-height: 1.45;
}

.quiz-key-explanation {
  margin: var(--space-3) 0 0;
  padding-top: var(--space-3);
  border-top: 1px solid var(--slate-650);
  font-size: var(--label);
  line-height: 1.5;
  color: var(--text-secondary);
}

/* ——— Lesson sequence nav ——— */
.lesson-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-4);
  margin-top: var(--space-16);
  padding-top: var(--space-10);
  border-top: 1px solid var(--slate-650);
}

.lesson-nav-link {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  min-height: 44px;
  padding: var(--space-5);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--paper-100);
  transition:
    border-color var(--transition-fast),
    background-color var(--transition-fast);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.lesson-nav-link:hover {
  border-color: var(--cyan-400);
  background: var(--hover-fill);
  text-decoration: none;
}

.lesson-nav-link:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

.lesson-nav-prev {
  align-items: flex-start;
}

.lesson-nav-next {
  align-items: flex-end;
  text-align: right;
  grid-column: 2;
}

.lesson-nav-prev:only-child {
  grid-column: 1;
}

.lesson-nav-next:only-child {
  grid-column: 2;
}

.lesson-nav-dir {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--amber-400);
}

.lesson-nav-label {
  font-family: var(--font-body);
  font-size: var(--label);
  font-weight: 500;
  color: var(--paper-100);
  line-height: 1.35;
}

.lesson-nav-num {
  font-family: var(--font-mono);
  color: var(--cyan-400);
  font-weight: 600;
  margin-right: var(--space-2);
}

.lesson-nav-disabled {
  opacity: 0.45;
  pointer-events: none;
  cursor: not-allowed;
}

/* ——— Lesson responsive ——— */
@media (max-width: 767px) {
  .lesson-page {
    padding-block: var(--space-6) var(--space-16);
  }

  .lesson-page > section + section,
  .lesson-page > header + section,
  .lesson-page > section + nav,
  .lesson-page > nav + section {
    margin-top: var(--space-12);
  }

  .lesson-masthead {
    grid-template-columns: 1fr;
    padding: var(--space-5);
    gap: var(--space-4);
  }

  .masthead-socket {
    width: 48px;
    height: 48px;
  }

  .example-card,
  .exercise-item,
  .quiz-question {
    padding: var(--space-4);
  }

  .lesson-nav {
    grid-template-columns: 1fr;
  }

  .lesson-nav-next,
  .lesson-nav-next:only-child,
  .lesson-nav-prev:only-child {
    grid-column: 1;
    align-items: flex-start;
    text-align: left;
  }

  .objectives-list > li {
    padding: var(--space-3) var(--space-4);
  }
}

@media (max-width: 419px) {
  .masthead-meta {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-3);
  }

  .meta-sep {
    display: none;
  }

  .quiz-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .quiz-submit,
  .quiz-reset {
    width: 100%;
  }
}

/* ——— Lesson print ——— */
@media print {
  .lesson-page {
    padding: 0;
    color: #000;
    background: #fff;
  }

  .site-header,
  .site-footer,
  .skip-link,
  .nav-toggle,
  .code-copy,
  .quiz-actions {
    display: none !important;
  }

  .lesson-masthead,
  .example-card,
  .exercise-item,
  .pitfall-item,
  .definition-square,
  .quiz-question,
  .quiz-score,
  .quiz-key-item,
  .objectives-list > li {
    background: #fff !important;
    border-color: #999 !important;
    box-shadow: none !important;
    color: #000;
    break-inside: avoid;
  }

  .definition-square::before {
    border-color: #bbb !important;
  }

  .definition-square-term,
  .definition-square-label {
    color: #000 !important;
  }

  .definition-square-body {
    color: #222 !important;
  }

  .masthead-title,
  .section-heading,
  .theory-title,
  .example-title,
  .exercise-title,
  .pitfall-title,
  .quiz-prompt {
    color: #000 !important;
  }

  .reading-column > p,
  .pitfall-body,
  .section-lead,
  .quiz-score-summary,
  .quiz-key-explanation {
    color: #222 !important;
  }

  .code-panel,
  .table-scroll,
  .video-frame {
    break-inside: avoid;
    border-color: #999 !important;
  }

  .code-panel pre,
  .result-table {
    white-space: pre-wrap;
    overflow: visible !important;
  }

  .lesson-nav-link {
    border-color: #999 !important;
    color: #000 !important;
  }

  a {
    color: #000 !important;
    text-decoration: underline;
  }

  .video-frame iframe {
    display: none;
  }
}

/* ==========================================================================
   Final exam page — graph-blueprint components
   Append-only; does not regress homepage/lesson styles above.
   ========================================================================== */

.exam-page {
  padding-block: var(--space-8) var(--space-20);
}

.exam-page > .container {
  width: 100%;
  max-width: var(--content-max);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.exam-intro {
  padding: var(--space-8);
  margin-bottom: var(--space-12);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exam-kicker {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--amber-400);
  margin-bottom: var(--space-2);
}

.exam-title {
  font-family: var(--font-display);
  font-size: var(--heading-1);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.08;
  color: var(--paper-100);
  margin-bottom: var(--space-4);
}

.exam-lead {
  max-width: 720px;
  font-size: var(--body-lg);
  line-height: 1.55;
  color: var(--text-secondary);
  margin-bottom: var(--space-6);
}

.exam-lead strong {
  color: var(--paper-100);
  font-weight: 600;
}

.exam-scope {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3) var(--space-6);
  margin: 0;
  padding: 0;
  list-style: none;
  font-family: var(--font-mono);
  font-size: var(--micro);
  color: var(--text-muted);
}

.exam-scope li {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  min-height: 32px;
}

.exam-scope li::before {
  content: "";
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--cyan-400);
  flex-shrink: 0;
}

.exam-section {
  border-top: 1px solid var(--slate-650);
  padding-top: var(--space-12);
}

.exam-mount {
  max-width: 720px;
  margin-top: var(--space-6);
}

.exam-root {
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
}

.exam-loading,
.exam-status {
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--text-muted);
  margin: 0;
}

.exam-error {
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-left: 3px solid var(--amber-400);
  border-radius: var(--radius-sm);
  color: var(--paper-100);
  font-size: var(--body);
  line-height: 1.55;
}

.exam-progress-bar {
  position: sticky;
  top: var(--header-h);
  z-index: 40;
  padding: var(--space-4) var(--space-5);
  background: rgba(18, 24, 29, 0.96);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
  backdrop-filter: blur(8px);
}

.exam-progress-bar .exam-status {
  color: var(--paper-100);
  font-weight: 500;
}

.exam-weight-note {
  margin: var(--space-1) 0 0;
  font-family: var(--font-mono);
  font-size: var(--micro);
  color: var(--text-muted);
}

.exam-form {
  display: flex;
  flex-direction: column;
  gap: var(--space-6);
  margin: 0;
}

.exam-question {
  padding: var(--space-5) var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exam-question.is-correct {
  border-color: var(--cyan-400);
}

.exam-question.is-incorrect {
  border-color: var(--amber-400);
}

.exam-q-meta {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  margin-bottom: var(--space-3);
}

.exam-prompt {
  font-family: var(--font-body);
  font-size: var(--body);
  font-weight: 500;
  line-height: 1.5;
  color: var(--paper-100);
  margin: 0 0 var(--space-4);
}

.exam-choices {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.exam-choice {
  margin: 0;
}

.exam-choice label {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: var(--space-3);
  align-items: start;
  min-height: 48px;
  padding: var(--space-3) var(--space-4);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
  background: var(--graphite-950);
  cursor: pointer;
  color: var(--text-secondary);
  font-size: var(--body);
  line-height: 1.45;
  transition:
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.exam-choice label:hover {
  background: var(--hover-fill);
  border-color: rgba(57, 214, 232, 0.35);
}

.exam-choice input[type="radio"] {
  width: 18px;
  height: 18px;
  margin: 2px 0 0;
  accent-color: var(--cyan-400);
  flex-shrink: 0;
  cursor: pointer;
}

.exam-choice label:has(input[type="radio"]:focus-visible) {
  box-shadow: var(--focus-ring);
}

.exam-choice label:has(input[type="radio"]:checked) {
  border-color: var(--cyan-400);
  background: var(--hover-fill);
  color: var(--paper-100);
}

.exam-choice-text {
  min-width: 0;
}

.exam-question.is-locked .exam-choice label {
  cursor: default;
}

.exam-question.is-locked .exam-choice input[type="radio"] {
  cursor: default;
}

.exam-feedback {
  margin-top: var(--space-4);
  padding: var(--space-3) var(--space-4);
  font-size: var(--label);
  line-height: 1.45;
  border-radius: var(--radius-sm);
  border: 1px solid var(--slate-650);
  background: var(--graphite-950);
  color: var(--text-secondary);
}

.exam-feedback.is-correct {
  border-color: rgba(57, 214, 232, 0.45);
  color: var(--paper-100);
}

.exam-feedback.is-incorrect {
  border-color: rgba(231, 169, 59, 0.55);
  color: var(--paper-100);
}

.exam-feedback-status {
  margin: 0 0 var(--space-2);
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.exam-feedback.is-correct .exam-feedback-status {
  color: var(--cyan-400);
}

.exam-feedback.is-incorrect .exam-feedback-status {
  color: var(--amber-400);
}

.exam-feedback-detail,
.exam-feedback-explanation,
.exam-feedback-review {
  margin: var(--space-2) 0 0;
  color: var(--text-secondary);
  font-size: var(--label);
  line-height: 1.5;
}

.exam-feedback-explanation {
  padding-top: var(--space-3);
  border-top: 1px solid var(--slate-650);
  margin-top: var(--space-3);
}

.exam-review-link {
  color: var(--cyan-400);
  font-weight: 500;
}

.exam-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
  align-items: center;
}

.exam-submit,
.exam-reset {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: var(--control-h);
  min-width: 44px;
  padding: 0 var(--space-6);
  font-family: var(--font-body);
  font-size: var(--label);
  font-weight: 600;
  line-height: 1.2;
  border-radius: var(--radius-sm);
  transition:
    background-color var(--transition-fast),
    color var(--transition-fast),
    box-shadow var(--transition-fast),
    transform var(--transition-fast);
}

.exam-submit {
  background-color: var(--cyan-400);
  color: var(--graphite-950);
  box-shadow: inset 0 -2px 0 rgba(11, 15, 18, 0.18);
  border: none;
}

.exam-submit:hover:not(:disabled) {
  background-color: #4fdeec;
  box-shadow: inset 0 -1px 0 rgba(11, 15, 18, 0.18);
}

.exam-submit:active:not(:disabled) {
  transform: translateY(1px);
}

.exam-submit:focus-visible,
.exam-reset:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
}

.exam-submit:disabled {
  opacity: 0.55;
  cursor: not-allowed;
  transform: none;
}

.exam-reset {
  background: transparent;
  color: var(--cyan-400);
  border: 1px solid var(--slate-650);
}

.exam-reset:hover {
  background: var(--hover-fill);
  border-color: var(--cyan-400);
}

/* Score */
.exam-results {
  display: flex;
  flex-direction: column;
  gap: var(--space-8);
}

.exam-score {
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exam-score:focus {
  outline: none;
  box-shadow: var(--focus-ring);
}

.exam-score-headline {
  font-family: var(--font-mono);
  font-size: var(--label);
  font-weight: 600;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--amber-400);
  margin: 0 0 var(--space-3);
}

.exam-score-value {
  font-family: var(--font-display);
  font-size: var(--display-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1;
  color: var(--paper-100);
  margin: 0 0 var(--space-2);
}

.exam-score-fraction {
  font-family: var(--font-mono);
  font-size: 0.85em;
  color: var(--cyan-400);
  font-weight: 600;
}

.exam-score-percent,
.exam-score-count,
.exam-score-summary {
  margin: 0 0 var(--space-2);
  font-size: var(--body);
  color: var(--text-secondary);
  line-height: 1.55;
}

.exam-score-summary {
  margin-bottom: 0;
  margin-top: var(--space-3);
  padding-top: var(--space-3);
  border-top: 1px solid var(--slate-650);
}

/* Certificate (screen + print sheet) */
.exam-certificate {
  padding: var(--space-8);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.exam-certificate-form {
  display: flex;
  flex-direction: column;
  gap: var(--space-5);
  margin-bottom: var(--space-8);
  max-width: 480px;
}

.exam-certificate-field {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.exam-certificate-label {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.exam-certificate-input {
  min-height: var(--control-h);
  padding: 0 var(--space-4);
  font-family: var(--font-body);
  font-size: var(--body);
  color: var(--paper-100);
  background: var(--graphite-950);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-sm);
}

.exam-certificate-input::placeholder {
  color: var(--text-muted);
}

.exam-certificate-input:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-color: var(--cyan-400);
}

.exam-certificate-input[aria-invalid="true"] {
  border-color: var(--amber-400);
}

.exam-certificate-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
}

.exam-print-btn {
  border: none;
  cursor: pointer;
}

.certificate-sheet {
  padding: var(--space-10) var(--space-8);
  background: var(--graphite-950);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  text-align: center;
  box-shadow: inset 0 0 0 1px rgba(57, 214, 232, 0.12);
}

.certificate-brand {
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--cyan-400);
  margin: 0 0 var(--space-4);
}

.certificate-title {
  font-family: var(--font-display);
  font-size: var(--heading-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--paper-100);
  margin: 0 0 var(--space-6);
}

.certificate-award {
  font-size: var(--label);
  color: var(--text-muted);
  margin: 0 0 var(--space-2);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  font-family: var(--font-mono);
}

.certificate-name {
  font-family: var(--font-display);
  font-size: var(--display-2);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.1;
  color: var(--paper-100);
  margin: 0 0 var(--space-4);
  min-height: 1.2em;
}

.certificate-body {
  max-width: 40ch;
  margin: 0 auto var(--space-8);
  font-size: var(--body);
  line-height: 1.55;
  color: var(--text-secondary);
}

.certificate-meta {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: var(--space-2) var(--space-5);
  max-width: 480px;
  margin: 0 auto var(--space-8);
  text-align: left;
}

.certificate-meta dt {
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--amber-400);
  margin: 0;
  padding-top: 2px;
}

.certificate-meta dd {
  font-family: var(--font-mono);
  font-size: var(--label);
  color: var(--paper-100);
  margin: 0;
  line-height: 1.45;
}

.certificate-seal {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--micro);
  color: var(--text-muted);
  letter-spacing: 0.04em;
}

/* Exam responsive */
@media (max-width: 767px) {
  .exam-page {
    padding-block: var(--space-6) var(--space-16);
  }

  .exam-intro {
    padding: var(--space-5);
  }

  .exam-question {
    padding: var(--space-4);
  }

  .exam-progress-bar {
    top: var(--header-h);
  }

  .exam-certificate {
    padding: var(--space-5);
  }

  .certificate-sheet {
    padding: var(--space-6) var(--space-4);
  }

  .certificate-meta {
    grid-template-columns: 1fr;
    gap: var(--space-1) 0;
  }

  .certificate-meta dd {
    margin-bottom: var(--space-3);
  }
}

@media (max-width: 419px) {
  .exam-actions {
    flex-direction: column;
    align-items: stretch;
  }

  .exam-submit,
  .exam-reset,
  .exam-print-btn {
    width: 100%;
  }
}

/* ——— Exam print: certificate only ——— */
@media print {
  body.printing-certificate * {
    visibility: hidden !important;
  }

  body.printing-certificate .certificate-sheet,
  body.printing-certificate .certificate-sheet * {
    visibility: visible !important;
  }

  body.printing-certificate .certificate-sheet {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    max-width: none;
    margin: 0;
    padding: 48px 40px;
    background: #fff !important;
    border: 2px solid #29343c !important;
    border-radius: 0 !important;
    box-shadow: none !important;
    color: #0b0f12 !important;
    -webkit-print-color-adjust: exact;
    print-color-adjust: exact;
  }

  body.printing-certificate .site-header,
  body.printing-certificate .site-footer,
  body.printing-certificate .skip-link,
  body.printing-certificate .exam-intro,
  body.printing-certificate .exam-form,
  body.printing-certificate .exam-progress-bar,
  body.printing-certificate .exam-score,
  body.printing-certificate .exam-certificate-form,
  body.printing-certificate .exam-actions,
  body.printing-certificate .nav-toggle {
    display: none !important;
  }

  body.printing-certificate .certificate-brand {
    color: #0b0f12 !important;
  }

  body.printing-certificate .certificate-title,
  body.printing-certificate .certificate-name {
    color: #0b0f12 !important;
  }

  body.printing-certificate .certificate-award,
  body.printing-certificate .certificate-body,
  body.printing-certificate .certificate-seal {
    color: #29343c !important;
  }

  body.printing-certificate .certificate-meta dt {
    color: #0b0f12 !important;
  }

  body.printing-certificate .certificate-meta dd {
    color: #0b0f12 !important;
  }

  body.printing-certificate .exam-page,
  body.printing-certificate .exam-certificate,
  body.printing-certificate .exam-results,
  body.printing-certificate main {
    background: #fff !important;
    padding: 0 !important;
    margin: 0 !important;
    border: none !important;
    box-shadow: none !important;
  }
}

/* ——— Resources page (hub) ——— */
.resources-page {
  padding-block: var(--space-10) var(--space-24);
}

.resources-page > .container {
  max-width: var(--content-max);
}

.resources-intro {
  margin-bottom: var(--space-16);
  padding-bottom: var(--space-10);
  border-bottom: 1px solid var(--slate-650);
}

.resources-kicker {
  margin: 0 0 var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--amber-400);
}

.resources-title {
  margin: 0 0 var(--space-5);
  font-family: var(--font-display);
  font-size: var(--heading-1);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.08;
  color: var(--paper-100);
}

.resources-lead {
  margin: 0 0 var(--space-8);
  max-width: 720px;
  font-size: var(--body-lg);
  line-height: 1.55;
  color: var(--text-secondary);
}

.resources-jump {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-5);
  font-family: var(--font-mono);
  font-size: var(--label);
  line-height: 1.35;
}

.resources-jump a {
  color: var(--cyan-400);
  text-decoration: none;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  border-bottom: 1px solid transparent;
}

.resources-jump a:hover {
  border-bottom-color: var(--cyan-400);
}

.resources-jump a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.resources-section {
  margin-bottom: var(--space-16);
  scroll-margin-top: calc(var(--header-h) + var(--space-6));
}

.resources-section .section-heading {
  margin-bottom: var(--space-3);
}

.resources-section .section-lead {
  margin-bottom: var(--space-8);
}

.resource-card-grid {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-5);
}

@media (min-width: 768px) {
  .resource-card-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: var(--space-6);
  }
}

@media (min-width: 1200px) {
  .resource-card-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .resource-card-grid--video {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

.resource-card {
  height: 100%;
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  padding: var(--space-6);
  background: var(--graphite-850);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
  transition:
    border-color var(--transition-fast),
    background-color var(--transition-fast);
}

.resource-card:hover,
.resource-card:focus-within {
  border-color: var(--cyan-400);
  background: color-mix(in srgb, var(--graphite-850) 92%, var(--cyan-400) 8%);
}

.resource-card-meta {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--micro);
  font-weight: 500;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--amber-400);
}

.resource-card-title {
  margin: 0;
  font-family: var(--font-display);
  font-size: var(--heading-3);
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

.resource-card-title a {
  color: var(--paper-100);
  text-decoration: none;
}

.resource-card-title a:hover {
  color: var(--cyan-400);
  text-decoration: underline;
  text-underline-offset: 0.15em;
}

.resource-card-title a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.resource-card-desc {
  margin: 0;
  flex: 1 1 auto;
  font-size: var(--body);
  line-height: 1.55;
  color: var(--text-secondary);
}

.resource-card-lessons {
  margin: var(--space-2) 0 0;
  padding-top: var(--space-3);
  border-top: 1px solid rgba(41, 52, 60, 0.75);
  font-family: var(--font-mono);
  font-size: var(--micro);
  line-height: 1.45;
  color: var(--text-muted);
}

.resource-card-lessons a {
  color: var(--cyan-400);
  text-decoration: none;
}

.resource-card-lessons a:hover {
  text-decoration: underline;
  text-underline-offset: 0.15em;
}

.resource-card-lessons a:focus-visible {
  outline: none;
  box-shadow: var(--focus-ring);
  border-radius: var(--radius-sm);
}

.resources-footnote {
  margin-top: var(--space-8);
  padding: var(--space-6);
  border: 1px solid var(--slate-650);
  border-radius: var(--radius-md);
  background: var(--graphite-850);
  box-shadow: inset 0 1px 0 var(--inset-highlight);
}

.resources-footnote p {
  margin: 0;
  max-width: 720px;
  font-size: var(--label);
  line-height: 1.5;
  color: var(--text-muted);
}

.resources-footnote code {
  font-family: var(--font-mono);
  font-size: 0.92em;
  color: var(--cyan-400);
}

@media (max-width: 767px) {
  .resources-page {
    padding-block: var(--space-8) var(--space-16);
  }

  .resource-card {
    padding: var(--space-5);
  }

  .resources-intro {
    margin-bottom: var(--space-12);
  }
}