/* ============================================================
   INFINITE RUNNER TUTORIAL - STYLE SYSTEM
   A distinctive, production-grade tutorial site.
   Dark-first with light toggle. No generic AI aesthetics.
   ============================================================ */

/* --- CSS Custom Properties (Themes) --- */
:root {
  /* Dark theme (default) */
  --bg-primary: #0a0e1a;
  --bg-secondary: #111827;
  --bg-tertiary: #1a2035;
  --bg-card: #151c2e;
  --bg-code: #0d1117;
  --bg-sidebar: #0c1120;
  --bg-hover: #1e2a45;
  --bg-active: #1a2744;

  --text-primary: #e2e8f0;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --text-inverse: #0a0e1a;

  --accent: #06d6a0;
  --accent-hover: #05c495;
  --accent-glow: rgba(6, 214, 160, 0.15);
  --accent-secondary: #7c3aed;
  --accent-tertiary: #f59e0b;
  --accent-danger: #ef4444;

  --border: #1e293b;
  --border-light: #2d3a52;
  --border-accent: rgba(6, 214, 160, 0.3);

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.3);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.4);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
  --shadow-glow: 0 0 20px rgba(6, 214, 160, 0.1);

  --callout-tip-bg: rgba(6, 214, 160, 0.08);
  --callout-tip-border: #06d6a0;
  --callout-warn-bg: rgba(245, 158, 11, 0.08);
  --callout-warn-border: #f59e0b;
  --callout-info-bg: rgba(59, 130, 246, 0.08);
  --callout-info-border: #3b82f6;
  --callout-danger-bg: rgba(239, 68, 68, 0.08);
  --callout-danger-border: #ef4444;

  --sidebar-width: 300px;
  --topbar-height: 60px;
  --content-max-width: 860px;

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace;

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;

  --transition-fast: 150ms ease;
  --transition-normal: 250ms ease;
  --transition-slow: 400ms ease;
}

[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --bg-code: #f6f8fa;
  --bg-sidebar: #ffffff;
  --bg-hover: #e2e8f0;
  --bg-active: #dbeafe;

  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --text-inverse: #f8fafc;

  --accent: #059669;
  --accent-hover: #047857;
  --accent-glow: rgba(5, 150, 105, 0.1);
  --accent-secondary: #7c3aed;

  --border: #e2e8f0;
  --border-light: #cbd5e1;
  --border-accent: rgba(5, 150, 105, 0.3);

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.1);
  --shadow-glow: 0 0 20px rgba(5, 150, 105, 0.06);

  --callout-tip-bg: rgba(5, 150, 105, 0.06);
  --callout-warn-bg: rgba(245, 158, 11, 0.06);
  --callout-info-bg: rgba(59, 130, 246, 0.06);
  --callout-danger-bg: rgba(239, 68, 68, 0.06);
}

/* --- Reset & Base --- */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--font-sans);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  min-height: 100vh;
  transition: background var(--transition-normal), color var(--transition-normal);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

a {
  color: var(--accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-hover);
}

img {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius-md);
}

::selection {
  background: var(--accent);
  color: var(--text-inverse);
}

/* --- Scrollbar --- */
::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: var(--bg-primary);
}

::-webkit-scrollbar-thumb {
  background: var(--border-light);
  border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

/* --- Reading Progress Bar --- */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent-secondary));
  z-index: 1001;
  transition: width 100ms linear;
}

/* ============================================================
   TOP BAR
   ============================================================ */
.topbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--topbar-height);
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 1.5rem;
  z-index: 100;
  backdrop-filter: blur(12px);
  transition: background var(--transition-normal), border-color var(--transition-normal);
}

.topbar-left {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.topbar-logo {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--text-primary);
  letter-spacing: -0.02em;
}

.topbar-logo .logo-icon {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--accent), var(--accent-secondary));
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1rem;
  color: white;
  font-weight: 800;
}

.topbar-right {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

/* Sidebar toggle (mobile) */
.sidebar-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  cursor: pointer;
  padding: 0.4rem;
  border-radius: var(--radius-sm);
  transition: background var(--transition-fast);
}

.sidebar-toggle:hover {
  background: var(--bg-hover);
}

.sidebar-toggle svg {
  width: 24px;
  height: 24px;
}

/* Theme toggle */
.theme-toggle {
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-primary);
  cursor: pointer;
  padding: 0.45rem 0.7rem;
  border-radius: 50px;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-size: 0.8rem;
  font-family: var(--font-sans);
  transition: all var(--transition-fast);
}

.theme-toggle:hover {
  background: var(--bg-hover);
  border-color: var(--border-light);
}

.theme-toggle .theme-icon {
  font-size: 1rem;
  line-height: 1;
}

/* ============================================================
   SIDEBAR
   ============================================================ */
.sidebar {
  position: fixed;
  top: var(--topbar-height);
  left: 0;
  width: var(--sidebar-width);
  height: calc(100vh - var(--topbar-height));
  background: var(--bg-sidebar);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  padding: 1.25rem 0;
  z-index: 50;
  transition: transform var(--transition-normal), background var(--transition-normal);
}

.sidebar-section {
  margin-bottom: 0.5rem;
}

.sidebar-section-title {
  padding: 0.5rem 1.25rem;
  font-size: 0.65rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--text-muted);
}

.sidebar-link {
  display: flex;
  align-items: flex-start;
  gap: 0.6rem;
  padding: 0.5rem 1.25rem;
  color: var(--text-secondary);
  font-size: 0.875rem;
  line-height: 1.4;
  transition: all var(--transition-fast);
  border-left: 3px solid transparent;
  text-decoration: none;
}

.sidebar-link:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
}

.sidebar-link.active {
  color: var(--accent);
  background: var(--accent-glow);
  border-left-color: var(--accent);
  font-weight: 500;
}

.sidebar-link .chapter-num {
  flex-shrink: 0;
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--text-muted);
  background: var(--bg-tertiary);
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
  margin-top: 0.1rem;
  font-family: var(--font-mono);
}

.sidebar-link.active .chapter-num {
  background: var(--accent);
  color: var(--text-inverse);
}

/* ============================================================
   MAIN CONTENT
   ============================================================ */
.main-content {
  margin-left: var(--sidebar-width);
  margin-top: var(--topbar-height);
  min-height: calc(100vh - var(--topbar-height));
  padding: 2.5rem 3rem 4rem;
  transition: margin var(--transition-normal);
}

.content-wrapper {
  max-width: var(--content-max-width);
  margin: 0 auto;
}

/* ============================================================
   LANDING PAGE
   ============================================================ */
.hero {
  text-align: center;
  padding: 4rem 0 3rem;
}

.hero-badge {
  display: inline-block;
  padding: 0.35rem 1rem;
  background: var(--accent-glow);
  border: 1px solid var(--border-accent);
  border-radius: 50px;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--accent);
  margin-bottom: 1.5rem;
  letter-spacing: 0.02em;
}

.hero h1 {
  font-size: clamp(2.2rem, 5vw, 3.5rem);
  font-weight: 800;
  line-height: 1.15;
  letter-spacing: -0.03em;
  margin-bottom: 1.25rem;
  background: linear-gradient(135deg, var(--text-primary) 0%, var(--accent) 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero p {
  font-size: 1.15rem;
  color: var(--text-secondary);
  max-width: 600px;
  margin: 0 auto 2rem;
  line-height: 1.7;
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.85rem 2rem;
  background: var(--accent);
  color: var(--text-inverse);
  font-weight: 700;
  font-size: 1rem;
  border-radius: 50px;
  transition: all var(--transition-fast);
  box-shadow: 0 4px 20px rgba(6, 214, 160, 0.25);
}

.hero-cta:hover {
  background: var(--accent-hover);
  color: var(--text-inverse);
  transform: translateY(-2px);
  box-shadow: 0 6px 28px rgba(6, 214, 160, 0.35);
}

.hero-stats {
  display: flex;
  justify-content: center;
  gap: 3rem;
  margin-top: 3rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
}

.hero-stat {
  text-align: center;
}

.hero-stat .stat-value {
  font-size: 1.8rem;
  font-weight: 800;
  color: var(--accent);
  letter-spacing: -0.02em;
}

.hero-stat .stat-label {
  font-size: 0.8rem;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-top: 0.2rem;
}

/* Feature cards */
.features-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1.25rem;
  margin: 3rem 0;
}

.feature-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  transition: all var(--transition-fast);
}

.feature-card:hover {
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow);
  transform: translateY(-2px);
}

.feature-card .feature-icon {
  width: 40px;
  height: 40px;
  border-radius: var(--radius-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.2rem;
  margin-bottom: 0.75rem;
}

.feature-card .feature-icon.green { background: rgba(6, 214, 160, 0.12); }
.feature-card .feature-icon.purple { background: rgba(124, 58, 237, 0.12); }
.feature-card .feature-icon.yellow { background: rgba(245, 158, 11, 0.12); }
.feature-card .feature-icon.blue { background: rgba(59, 130, 246, 0.12); }

.feature-card h3 {
  font-size: 1rem;
  font-weight: 700;
  margin-bottom: 0.4rem;
}

.feature-card p {
  font-size: 0.875rem;
  color: var(--text-secondary);
  line-height: 1.55;
}

/* Chapter list on landing */
.chapter-list-section {
  margin: 3rem 0;
}

.chapter-list-section h2 {
  font-size: 1.6rem;
  font-weight: 800;
  margin-bottom: 0.5rem;
  letter-spacing: -0.02em;
}

.chapter-list-section > p {
  color: var(--text-secondary);
  margin-bottom: 2rem;
}

.part-group {
  margin-bottom: 2rem;
}

.part-title {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent);
  margin-bottom: 0.75rem;
  padding-left: 0.25rem;
}

.chapter-card {
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0.9rem 1.1rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  margin-bottom: 0.5rem;
  transition: all var(--transition-fast);
  text-decoration: none;
  color: var(--text-primary);
}

.chapter-card:hover {
  border-color: var(--border-accent);
  background: var(--bg-hover);
  color: var(--text-primary);
  transform: translateX(4px);
}

.chapter-card .ch-number {
  flex-shrink: 0;
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-tertiary);
  border-radius: var(--radius-sm);
  font-size: 0.8rem;
  font-weight: 700;
  font-family: var(--font-mono);
  color: var(--text-muted);
}

.chapter-card:hover .ch-number {
  background: var(--accent);
  color: var(--text-inverse);
}

.chapter-card .ch-info h3 {
  font-size: 0.95rem;
  font-weight: 600;
  margin-bottom: 0.15rem;
}

.chapter-card .ch-info p {
  font-size: 0.8rem;
  color: var(--text-muted);
  line-height: 1.4;
}

.chapter-card .ch-arrow {
  margin-left: auto;
  color: var(--text-muted);
  transition: transform var(--transition-fast);
  flex-shrink: 0;
}

.chapter-card:hover .ch-arrow {
  transform: translateX(4px);
  color: var(--accent);
}

/* ============================================================
   CHAPTER PAGE TYPOGRAPHY
   ============================================================ */
.chapter-header {
  margin-bottom: 2.5rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--border);
}

.chapter-header .chapter-label {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--accent);
  margin-bottom: 0.75rem;
}

.chapter-header h1 {
  font-size: clamp(1.8rem, 4vw, 2.5rem);
  font-weight: 800;
  line-height: 1.2;
  letter-spacing: -0.03em;
  margin-bottom: 0.75rem;
}

.chapter-header .chapter-desc {
  font-size: 1.1rem;
  color: var(--text-secondary);
  line-height: 1.6;
}

.chapter-header .chapter-meta {
  display: flex;
  gap: 1.5rem;
  margin-top: 1rem;
  font-size: 0.8rem;
  color: var(--text-muted);
}

.chapter-header .chapter-meta span {
  display: flex;
  align-items: center;
  gap: 0.3rem;
}

/* Content typography */
.content-wrapper h2 {
  font-size: 1.5rem;
  font-weight: 700;
  margin-top: 3rem;
  margin-bottom: 1rem;
  letter-spacing: -0.02em;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

.content-wrapper h3 {
  font-size: 1.2rem;
  font-weight: 700;
  margin-top: 2rem;
  margin-bottom: 0.75rem;
  letter-spacing: -0.01em;
}

.content-wrapper h4 {
  font-size: 1.05rem;
  font-weight: 600;
  margin-top: 1.5rem;
  margin-bottom: 0.5rem;
}

.content-wrapper p {
  margin-bottom: 1rem;
  color: var(--text-primary);
}

.content-wrapper ul, .content-wrapper ol {
  margin-bottom: 1rem;
  padding-left: 1.5rem;
}

.content-wrapper li {
  margin-bottom: 0.4rem;
  color: var(--text-primary);
}

.content-wrapper strong {
  font-weight: 600;
  color: var(--text-primary);
}

.content-wrapper em {
  color: var(--text-secondary);
}

/* Inline code */
.content-wrapper code:not([class*="language-"]) {
  font-family: var(--font-mono);
  font-size: 0.85em;
  background: var(--bg-tertiary);
  color: var(--accent);
  padding: 0.15rem 0.4rem;
  border-radius: 4px;
  border: 1px solid var(--border);
}

/* ============================================================
   CODE BLOCKS
   ============================================================ */
.code-block {
  position: relative;
  margin: 1.25rem 0 1.5rem;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 1px solid var(--border);
  background: var(--bg-code);
}

.code-block-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.5rem 1rem;
  background: var(--bg-tertiary);
  border-bottom: 1px solid var(--border);
  font-size: 0.75rem;
}

.code-block-header .file-name {
  font-family: var(--font-mono);
  color: var(--text-secondary);
  font-weight: 500;
}

.code-block-header .lang-badge {
  font-family: var(--font-mono);
  color: var(--accent);
  font-weight: 600;
  text-transform: uppercase;
  font-size: 0.65rem;
  letter-spacing: 0.05em;
}

.copy-btn {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  background: var(--bg-tertiary);
  border: 1px solid var(--border);
  color: var(--text-muted);
  cursor: pointer;
  padding: 0.35rem 0.6rem;
  border-radius: var(--radius-sm);
  font-size: 0.7rem;
  font-family: var(--font-sans);
  display: flex;
  align-items: center;
  gap: 0.3rem;
  transition: all var(--transition-fast);
  z-index: 2;
  opacity: 0;
}

.code-block:hover .copy-btn {
  opacity: 1;
}

.copy-btn:hover {
  background: var(--bg-hover);
  color: var(--text-primary);
  border-color: var(--border-light);
}

.copy-btn.copied {
  background: var(--accent);
  color: var(--text-inverse);
  border-color: var(--accent);
}

.code-block pre {
  margin: 0;
  padding: 1.25rem;
  overflow-x: auto;
  font-size: 0.85rem;
  line-height: 1.65;
}

.code-block pre code {
  font-family: var(--font-mono);
  background: none;
  border: none;
  padding: 0;
}

/* With header, move copy button */
.code-block-header + pre + .copy-btn,
.code-block-header ~ .copy-btn {
  top: calc(0.5rem + 34px);
}

/* ============================================================
   CALLOUT BOXES
   ============================================================ */
.callout {
  padding: 1rem 1.25rem;
  border-radius: var(--radius-md);
  margin: 1.25rem 0;
  border-left: 4px solid;
  font-size: 0.9rem;
}

.callout-title {
  font-weight: 700;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: 0.4rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

.callout p {
  margin-bottom: 0.5rem;
  color: var(--text-primary);
}

.callout p:last-child {
  margin-bottom: 0;
}

.callout.tip {
  background: var(--callout-tip-bg);
  border-color: var(--callout-tip-border);
}
.callout.tip .callout-title { color: var(--callout-tip-border); }

.callout.warning {
  background: var(--callout-warn-bg);
  border-color: var(--callout-warn-border);
}
.callout.warning .callout-title { color: var(--callout-warn-border); }

.callout.info {
  background: var(--callout-info-bg);
  border-color: var(--callout-info-border);
}
.callout.info .callout-title { color: var(--callout-info-border); }

.callout.danger {
  background: var(--callout-danger-bg);
  border-color: var(--callout-danger-border);
}
.callout.danger .callout-title { color: var(--callout-danger-border); }

/* ============================================================
   STEP-BY-STEP INSTRUCTIONS
   ============================================================ */
.steps {
  counter-reset: step;
  list-style: none;
  padding: 0;
  margin: 1.25rem 0;
}

.steps li {
  counter-increment: step;
  position: relative;
  padding: 0.75rem 0 0.75rem 3rem;
  margin-bottom: 0.25rem;
}

.steps li::before {
  content: counter(step);
  position: absolute;
  left: 0;
  top: 0.65rem;
  width: 28px;
  height: 28px;
  background: var(--accent);
  color: var(--text-inverse);
  border-radius: 50%;
  font-size: 0.8rem;
  font-weight: 700;
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-mono);
}

.steps li::after {
  content: '';
  position: absolute;
  left: 13px;
  top: 2.4rem;
  bottom: -0.25rem;
  width: 2px;
  background: var(--border);
}

.steps li:last-child::after {
  display: none;
}

/* ============================================================
   CHAPTER NAVIGATION (prev/next)
   ============================================================ */
.chapter-nav {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
}

.chapter-nav a {
  display: block;
  padding: 1.1rem 1.25rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  transition: all var(--transition-fast);
  text-decoration: none;
}

.chapter-nav a:hover {
  border-color: var(--border-accent);
  box-shadow: var(--shadow-glow);
  transform: translateY(-2px);
}

.chapter-nav a .nav-label {
  display: block;
  font-size: 0.7rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--text-muted);
  margin-bottom: 0.3rem;
}

.chapter-nav a .nav-title {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-primary);
}

.chapter-nav .nav-next {
  text-align: right;
}

.chapter-nav .nav-prev:empty,
.chapter-nav .nav-next:empty {
  visibility: hidden;
}

/* ============================================================
   TABLES
   ============================================================ */
.content-wrapper table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.25rem 0;
  font-size: 0.9rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.content-wrapper th {
  background: var(--bg-tertiary);
  font-weight: 600;
  text-align: left;
  padding: 0.75rem 1rem;
  border-bottom: 2px solid var(--border);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-secondary);
}

.content-wrapper td {
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--border);
}

.content-wrapper tr:last-child td {
  border-bottom: none;
}

.content-wrapper tr:hover td {
  background: var(--bg-hover);
}

/* ============================================================
   ARCHITECTURE DIAGRAM (ASCII-art box)
   ============================================================ */
.diagram {
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  padding: 1.5rem;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  line-height: 1.5;
  color: var(--accent);
  margin: 1.25rem 0;
  white-space: pre;
}

/* ============================================================
   FOOTER
   ============================================================ */
.site-footer {
  margin-top: 4rem;
  padding: 2rem 0;
  border-top: 1px solid var(--border);
  text-align: center;
  color: var(--text-muted);
  font-size: 0.8rem;
}

/* ============================================================
   LANDING - NO SIDEBAR LAYOUT
   ============================================================ */
body.landing .main-content {
  margin-left: 0;
}

body.landing .sidebar {
  display: none;
}

/* ============================================================
   RESPONSIVE
   ============================================================ */
@media (max-width: 1024px) {
  .sidebar {
    transform: translateX(-100%);
  }

  .sidebar.open {
    transform: translateX(0);
    box-shadow: var(--shadow-lg);
  }

  .main-content {
    margin-left: 0;
  }

  .sidebar-toggle {
    display: flex;
  }

  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 40;
  }

  .sidebar-overlay.active {
    display: block;
  }
}

@media (max-width: 768px) {
  .main-content {
    padding: 1.5rem 1.25rem 3rem;
  }

  .hero h1 {
    font-size: 1.8rem;
  }

  .hero-stats {
    flex-direction: column;
    gap: 1rem;
  }

  .features-grid {
    grid-template-columns: 1fr;
  }

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

  .chapter-header .chapter-meta {
    flex-direction: column;
    gap: 0.4rem;
  }

  .code-block pre {
    font-size: 0.78rem;
    padding: 1rem;
  }
}

@media (max-width: 480px) {
  .topbar {
    padding: 0 1rem;
  }

  .topbar-logo span {
    display: none;
  }

  .hero-cta {
    width: 100%;
    justify-content: center;
  }

  .chapter-card {
    padding: 0.75rem;
  }
}

/* ============================================================
   PRISM.JS OVERRIDES (dark theme)
   ============================================================ */
pre[class*="language-"],
code[class*="language-"] {
  color: #e2e8f0;
  font-family: var(--font-mono);
  text-shadow: none;
}

.token.comment,
.token.prolog,
.token.doctype,
.token.cdata {
  color: #6b7280;
}

.token.punctuation {
  color: #94a3b8;
}

.token.property,
.token.tag,
.token.boolean,
.token.number,
.token.constant,
.token.symbol {
  color: #f59e0b;
}

.token.selector,
.token.attr-name,
.token.string,
.token.char,
.token.builtin {
  color: #06d6a0;
}

.token.operator,
.token.entity,
.token.url {
  color: #67e8f9;
}

.token.atrule,
.token.attr-value,
.token.keyword {
  color: #818cf8;
}

.token.function,
.token.class-name {
  color: #f472b6;
}

.token.regex,
.token.important,
.token.variable {
  color: #fbbf24;
}

/* Light theme Prism overrides */
[data-theme="light"] pre[class*="language-"],
[data-theme="light"] code[class*="language-"] {
  color: #1e293b;
}

[data-theme="light"] .token.comment { color: #6b7280; }
[data-theme="light"] .token.property,
[data-theme="light"] .token.number { color: #b45309; }
[data-theme="light"] .token.string,
[data-theme="light"] .token.builtin { color: #047857; }
[data-theme="light"] .token.keyword { color: #6d28d9; }
[data-theme="light"] .token.function,
[data-theme="light"] .token.class-name { color: #be185d; }
[data-theme="light"] .token.operator { color: #0e7490; }

/* ============================================================
   UTILITY CLASSES
   ============================================================ */
.text-accent { color: var(--accent); }
.text-muted { color: var(--text-muted); }
.mt-2 { margin-top: 2rem; }
.mb-2 { margin-bottom: 2rem; }
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}