/* ==========================================================================
   Leapfrog — Minimal Academic Design System
   ========================================================================== */

/* --- Tokens --- */
:root {
  --color-bg: #030712;
  --color-bg-alt: #0f172a;
  --color-text: #f9fafb;
  --color-text-secondary: #9ca3af;
  --color-text-muted: #6b7280;

  --color-accent: #22d3ee;
  /* High-Voltage Cyan */
  --color-accent-glow: rgba(34, 211, 238, 0.4);
  --color-success: #10b981;
  /* Grid Emerald */
  --color-warning: #f59e0b;
  /* Market Amber */

  --color-border: rgba(255, 255, 255, 0.1);
  --color-border-bright: rgba(255, 255, 255, 0.2);

  --font-body: "Inter", system-ui, sans-serif;
  --font-display: "Space Grotesk", sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, monospace;

  --measure: 44rem;
  --measure-wide: 64rem;
  --sidebar-width-collapsed: 5rem;
  --sidebar-width-expanded: 16rem;
  --sidebar-width: var(--sidebar-width-collapsed);

  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2.5rem;
  --space-2xl: 4rem;
  --space-3xl: 6rem;

  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;

  --bg-grid: linear-gradient(to right, rgba(255, 255, 255, 0.05) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(255, 255, 255, 0.05) 1px, transparent 1px);
}

/* --- Light Theme --- */
[data-theme="light"] {
  --color-bg: #f8fafc;
  --color-bg-alt: #e2e8f0;
  --color-text: #0f172a;
  --color-text-secondary: #475569;
  --color-text-muted: #94a3b8;

  --color-accent: #0891b2;
  --color-accent-glow: rgba(8, 145, 178, 0.25);
  --color-success: #059669;
  --color-warning: #d97706;

  --color-border: rgba(0, 0, 0, 0.1);
  --color-border-bright: rgba(0, 0, 0, 0.18);

  --bg-grid: linear-gradient(to right, rgba(0, 0, 0, 0.04) 1px, transparent 1px),
    linear-gradient(to bottom, rgba(0, 0, 0, 0.04) 1px, transparent 1px);
}

[data-theme="light"] .site-header {
  background: rgba(248, 250, 252, 0.95);
}

[data-theme="light"] pre {
  background: #e2e8f0 !important;
}

[data-theme="light"] code {
  background: rgba(0, 0, 0, 0.06);
}

[data-theme="light"] .mobile-nav {
  background: rgba(248, 250, 252, 0.85);
  border-color: var(--color-border-bright);
}

[data-theme="light"] .bento-card {
  background: rgba(0, 0, 0, 0.02);
}

[data-theme="light"] .bento-card:hover {
  background: rgba(0, 0, 0, 0.04);
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.08);
}

[data-theme="light"] .site-header:hover nav a {
  background: rgba(0, 0, 0, 0.04);
}

[data-theme="light"] .site-header nav a:hover {
  background: rgba(0, 0, 0, 0.06);
}

[data-theme="light"] .course-nav-link:hover {
  background: rgba(0, 0, 0, 0.04);
}

[data-theme="light"] .course-nav a {
  background: rgba(0, 0, 0, 0.02);
}

[data-theme="light"] .course-nav a:hover {
  background: rgba(0, 0, 0, 0.05);
}

[data-theme="light"] .search-overlay {
  background: rgba(0, 0, 0, 0.25);
}

[data-theme="light"] h1 {
  background: linear-gradient(to bottom right, #0f172a 40%, rgba(15, 23, 42, 0.5));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

[data-theme="light"] .prose blockquote {
  background: rgba(8, 145, 178, 0.06);
}

/* --- Theme Toggle --- */
.theme-toggle {
  background: none;
  border: none;
  cursor: pointer;
  color: var(--color-text-secondary);
  transition: all 0.2s ease;
  position: relative;
  width: 18px;
  height: 18px;
  padding: 0;
}

.theme-toggle:hover {
  color: var(--color-text);
}

.theme-toggle svg {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 18px;
  height: 18px;
  transition: opacity 0.3s ease, transform 0.4s cubic-bezier(0.4, 0, 0.2, 1);
}

.theme-toggle .icon-sun {
  opacity: 0;
  transform: translate(-50%, -50%) rotate(-90deg) scale(0.5);
}

.theme-toggle .icon-moon {
  opacity: 1;
  transform: translate(-50%, -50%) rotate(0deg) scale(1);
}

[data-theme="light"] .theme-toggle .icon-sun {
  opacity: 1;
  transform: translate(-50%, -50%) rotate(0deg) scale(1);
}

[data-theme="light"] .theme-toggle .icon-moon {
  opacity: 0;
  transform: translate(-50%, -50%) rotate(90deg) scale(0.5);
}

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

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  color: var(--color-text);
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.6;
  background: var(--color-bg);
  background-image: var(--bg-grid);
  background-size: 40px 40px;
  -webkit-font-smoothing: antialiased;
}

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

li {
  list-style: none;
  margin: 0;
  padding: 0;
}

.prose ul,
.prose ol {
  margin-bottom: var(--space-md);
  padding-left: var(--space-lg);
}

.prose ul li {
  list-style: disc;
  margin-bottom: var(--space-xs);
}

.prose ol li {
  list-style: decimal;
  margin-bottom: var(--space-xs);
}

/* --- Site Shell --- */
.site-shell {
  flex: 1;
  width: 100%;
  max-width: var(--measure-wide);
  margin: 0 auto;
  padding: 0 var(--space-lg);
  position: relative;
}

/* --- Skip Link --- */
.skip-link {
  position: absolute;
  top: -100%;
  left: var(--space-md);
  padding: var(--space-xs) var(--space-sm);
  background: var(--color-text);
  color: var(--color-bg);
  font-size: 0.875rem;
  text-decoration: none;
  z-index: 100;
  border-radius: 0 0 4px 4px;
}

.skip-link:focus {
  top: 0;
}

/* ==========================================================================
   Header & Navigation
   ========================================================================== */

.site-shell {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

@media (min-width: 1024px) {
  .site-shell {
    display: block;
    max-width: var(--measure-wide);
    margin: 0 0 0 var(--space-xl); /* Add some breathing room from the sidebar */
    width: auto;
    transition: margin-left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  }
  
  body {
    padding-left: var(--sidebar-width);
    transition: padding-left 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  }
}

.site-header {
  border-bottom: 1px solid var(--color-border);
  background: var(--color-bg);
  padding: var(--space-md) var(--space-lg);
  z-index: 100;
}

@media (min-width: 1024px) {
  .site-header {
    height: 100vh;
    width: var(--sidebar-width);
    position: fixed;
    left: 0 !important;
    top: 0 !important;
    margin: 0 !important;
    flex-direction: column;
    align-items: center;
    justify-content: flex-start;
    padding: var(--space-xl) 0;
    border-right: 1px solid var(--color-border);
    border-bottom: none;
    background: rgba(3, 7, 18, 0.9);
    backdrop-filter: blur(20px);
    overflow: hidden;
    z-index: 1000;
    transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  }

  .site-header:hover {
    --sidebar-width: var(--sidebar-width-expanded);
    overflow: visible; /* Allow content to overflow if necessary during expansion */
  }
}

.brand {
  color: var(--color-text);
  text-decoration: none;
  font-family: var(--font-display);
  font-size: 1.5rem;
  font-weight: 700;
  letter-spacing: -0.03em;
  display: flex;
  align-items: center;
  margin-bottom: var(--space-2xl);
  width: 100%;
  height: 48px;
  position: relative; /* Anchor for absolute children */
}

.brand svg {
  position: absolute;
  left: 40px;
  transform: translateX(-50%);
  flex-shrink: 0;
  transition: all 0.3s ease;
}

.nav-label {
  position: absolute;
  left: 80px; /* Locked outside the collapsed bar */
  opacity: 0;
  visibility: hidden;
  white-space: nowrap;
  transition: all 0.3s ease;
  pointer-events: none;
  color: var(--color-text);
}

.site-header:hover .nav-label {
  opacity: 1;
  visibility: visible;
  left: 64px; /* Move slightly into the expanded view */
  pointer-events: auto;
}

.site-header nav {
  display: none;
}

@media (min-width: 1024px) {
  .site-header nav {
    display: block;
    width: 100%;
  }

  .site-header nav ul {
    list-style: none !important;
    margin: 0 !important;
    padding: 0 !important;
    display: flex;
    flex-direction: column;
    gap: var(--space-xs);
  }

  .site-header nav li {
    list-style: none !important;
    margin: 0 !important;
    padding: 0 !important;
  }

  .site-header nav a {
    display: flex;
    align-items: center;
    padding: var(--space-sm) 0;
    font-size: 0.8125rem;
    color: var(--color-text-secondary);
    border-radius: var(--radius-md);
    transition: all 0.2s ease;
    width: 100%;
    height: 40px;
    position: relative;
  }

  .site-header nav a svg {
    position: absolute;
    left: 40px;
    transform: translateX(-50%);
    flex-shrink: 0;
  }

  .site-header:hover nav a {
    background: rgba(255, 255, 255, 0.05);
  }

  .site-header nav a:hover {
    background: rgba(255, 255, 255, 0.05);
    color: var(--color-text);
  }

  .site-header nav a.is-active {
    background: rgba(34, 211, 238, 0.1);
    color: var(--color-accent);
    box-shadow: 0 0 20px var(--color-accent-glow);
  }
}

/* Mobile Bottom Nav */
.mobile-nav {
  position: fixed;
  bottom: var(--space-md);
  left: 50%;
  transform: translateX(-50%);
  background: rgba(15, 23, 42, 0.8);
  backdrop-filter: blur(12px);
  border: 1px solid var(--color-border-bright);
  border-radius: 100px;
  padding: var(--space-xs) var(--space-md);
  display: flex;
  gap: var(--space-xs);
  z-index: 200;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
}

@media (min-width: 1024px) {
  .mobile-nav {
    display: none;
  }
}

.mobile-nav-link {
  padding: var(--space-sm);
  color: var(--color-text-secondary);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
}

.mobile-nav-link.is-active {
  color: var(--color-accent);
  background: rgba(34, 211, 238, 0.1);
}

.content-wrapper {
  flex: 1;
  display: flex;
  flex-direction: column;
}

@media (min-width: 1024px) {
  .content-wrapper {
    max-width: var(--measure-wide);
    margin: 0 auto;
    width: 100%;
    padding: 0 var(--space-2xl);
  }
}

.search-toggle {
  background: none;
  border: none;
  cursor: pointer;
  color: var(--color-text-secondary);
  transition: all 0.2s ease;
}

.search-toggle:hover {
  background: rgba(255, 255, 255, 0.05) !important;
  color: var(--color-text) !important;
}

.search-toggle svg {
  width: 1.25rem;
  height: 1.25rem;
  display: block;
}

/* Mobile toggle */
.nav-toggle {
  display: none;
}

.nav-toggle-label {
  display: none;
  cursor: pointer;
  padding: var(--space-xs);
  color: var(--color-text);
}

.nav-toggle-label svg {
  display: block;
  width: 1.5rem;
  height: 1.5rem;
}

/* ==========================================================================
   Main
   ========================================================================== */

.site-main {
  padding: var(--space-2xl) 0 var(--space-3xl);
}

/* ==========================================================================
   Footer
   ========================================================================== */

.site-footer {
  border-top: 1px solid var(--color-border);
  padding: var(--space-lg) var(--space-lg);
  text-align: center;
  color: var(--color-text-muted);
  font-size: 0.875rem;
}

.site-footer p {
  margin: 0;
}

/* ==========================================================================
   Typography
   ========================================================================== */

a {
  color: var(--color-accent);
  text-decoration-color: var(--color-border);
  text-underline-offset: 0.2em;
  transition: color 0.15s ease;
}

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

h1,
h2,
h3,
h4 {
  margin: 0;
  line-height: 1.2;
  font-family: var(--font-display);
  font-weight: 700;
  letter-spacing: -0.02em;
}

h1 {
  font-size: 3rem;
  background: linear-gradient(to bottom right, #fff 40%, rgba(255, 255, 255, 0.4));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
}

h2 {
  font-size: 1.875rem;
  color: var(--color-text);
}

h3 {
  font-size: 1.25rem;
}

h4 {
  font-size: 0.875rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: var(--color-text-secondary);
}

/* ==========================================================================
   Homepage Components
   ========================================================================== */

.hero-market {
  padding: var(--space-3xl) 0;
  max-width: 50rem;
}

.hero-market .badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-xs);
  padding: var(--space-xs) var(--space-md);
  background: rgba(34, 211, 238, 0.1);
  border: 1px solid rgba(34, 211, 238, 0.2);
  border-radius: 100px;
  color: var(--color-accent);
  font-size: 0.75rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  margin-bottom: var(--space-lg);
}

.hero-market h1 {
  margin-bottom: var(--space-md);
}

.hero-tagline {
  font-size: 1.25rem;
  color: var(--color-text-secondary);
  line-height: 1.6;
  max-width: 40rem;
}

/* Bento Grid */
.bento-grid {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: var(--space-md);
  margin-top: var(--space-2xl);
}

.bento-card {
  grid-column: span 12;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-lg);
  position: relative;
  overflow: hidden;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  display: flex;
  flex-direction: column;
}

.bento-card:hover {
  background: rgba(255, 255, 255, 0.04);
  border-color: var(--color-border-bright);
  transform: translateY(-4px);
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.4);
}

.bento-card .card-icon {
  width: 40px;
  height: 40px;
  background: rgba(34, 211, 238, 0.1);
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--color-accent);
  margin-bottom: var(--space-md);
}

.bento-card.featured {
  grid-column: span 12;
}

@media (min-width: 768px) {
  .bento-card {
    grid-column: span 6;
  }

  .bento-card.featured {
    grid-column: span 8;
  }

  .bento-card.compact {
    grid-column: span 4;
  }
}

.bento-card .meta {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-xs);
}

.bento-card h3 {
  margin-bottom: var(--space-sm);
}

.bento-card h3 a {
  color: inherit;
  text-decoration: none;
}

.bento-card p.summary {
  font-size: 0.9375rem;
  color: var(--color-text-secondary);
  margin: 0;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.bento-card .action {
  margin-top: auto;
  padding-top: var(--space-lg);
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--color-accent);
}

/* ==========================================================================
   Section Heading
   ========================================================================== */

.section-label {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  margin-bottom: var(--space-md);
}

.section-label .line {
  height: 1px;
  background: var(--color-border);
  flex: 1;
}

.section-label span {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  letter-spacing: 0.1em;
}

/* Tag list */
.search-results {
  list-style: none;
  margin: var(--space-lg) 0 0;
  padding: 0;
}

.search-results li {
  margin-bottom: var(--space-md);
}

.tag-list {
  list-style: none;
  margin: var(--space-lg) 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.tag-list a {
  display: inline-block;
  padding: var(--space-xs) var(--space-sm);
  border: 1px solid var(--color-border);
  border-radius: 3px;
  color: var(--color-text-secondary);
  font-size: 0.8125rem;
  text-decoration: none;
  transition: background-color 0.15s ease, border-color 0.15s ease;
}

.tag-list a:hover {
  background: var(--color-bg-subtle);
  border-color: var(--color-border);
  color: var(--color-text);
}

/* ==========================================================================
   Article (Single Page)
   ========================================================================== */

.article {
  max-width: var(--measure);
  margin: 0 auto;
}

.article-header {
  margin-bottom: var(--space-xl);
}

.article-header h1 {
  margin-bottom: var(--space-sm);
}

.article-header .meta {
  margin: 0;
  color: var(--color-text-muted);
  font-size: 0.875rem;
}

.back-link {
  display: inline-block;
  margin-bottom: var(--space-lg);
  color: var(--color-text-secondary);
  font-size: 0.875rem;
  text-decoration: none;
}

.back-link:hover {
  color: var(--color-accent);
}

/* ==========================================================================
   Prose (Article Content)
   ========================================================================== */

.prose {
  color: var(--color-text);
  font-size: 1.0625rem;
  line-height: 1.8;
}

.prose> :first-child {
  margin-top: 0;
}

.prose> :last-child {
  margin-bottom: 0;
}

.prose p,
.prose {
  color: var(--color-text-secondary);
  font-size: 1.0625rem;
  line-height: 1.8;
}

.prose h2 {
  color: var(--color-text);
  border-bottom: 1px solid var(--color-border);
  padding-bottom: var(--space-xs);
  margin-top: var(--space-2xl);
}

.prose h3 {
  color: var(--color-text);
  margin-top: var(--space-xl);
}

.prose a {
  color: var(--color-accent);
  text-decoration: none;
  border-bottom: 1px solid rgba(34, 211, 238, 0.3);
}

.prose a:hover {
  border-bottom-color: var(--color-accent);
}

.prose blockquote {
  border-left: 4px solid var(--color-accent);
  background: rgba(34, 211, 238, 0.05);
  margin: var(--space-xl) 0;
  padding: var(--space-md) var(--space-xl);
  color: var(--color-text);
  font-style: italic;
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
}

/* Code */
pre {
  background: #0f172a !important;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-md);
  margin: var(--space-xl) 0;
  overflow-x: auto;
}

code {
  font-family: var(--font-mono);
  font-size: 0.9em;
  background: rgba(255, 255, 255, 0.05);
  padding: 0.2em 0.4em;
  border-radius: var(--radius-sm);
}

pre code {
  background: none;
  padding: 0;
}

/* ==========================================================================
   List Page
   ========================================================================== */

.list-header {
  max-width: var(--measure);
  margin-bottom: var(--space-xl);
}

.list-header h1 {
  margin-bottom: var(--space-sm);
}

.list-header p {
  margin: 0;
  color: var(--color-text-secondary);
}

/* ==========================================================================
   Course Layout (Wider & Glued)
   ========================================================================== */

/* Remove constraints for course pages */
body:has(.course-layout) .site-shell {
  max-width: none;
  margin: 0;
  padding: 0;
}

body:has(.course-layout) .site-header,
body:has(.course-layout) .site-footer {
  max-width: var(--measure-wide);
  margin: 0 auto;
  padding-left: var(--space-lg);
  padding-right: var(--space-lg);
}

.course-layout {
  display: grid;
  grid-template-columns: 14rem 1fr;
  gap: var(--space-2xl);
  align-items: start;
}

.course-sidebar {
  position: sticky;
  top: var(--space-xl);
  height: auto;
  max-height: calc(100vh - var(--space-3xl));
  padding: 0;
  background: none;
  border-right: 1px solid var(--color-border);
  border-left: none;
  /* Sidebar on the left of content */
}

@media (max-width: 1024px) {
  .course-layout {
    grid-template-columns: 1fr;
  }

  .course-sidebar {
    order: 1;
    position: static;
    border-left: none;
    border-bottom: 1px solid var(--color-border);
    margin-bottom: var(--space-xl);
  }
}

.course-sidebar-title {
  font-family: var(--font-display);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--color-text-muted);
  text-decoration: none;
}

.course-nav-list {
  list-style: none !important;
  margin: 0 !important;
  padding: 0 !important;
}

.course-nav-item {
  list-style: none !important;
  margin: 0 !important;
  padding: 0 !important;
}

.course-nav-link {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  padding: var(--space-sm) var(--space-lg);
  color: var(--color-text-secondary);
  text-decoration: none;
  font-size: 0.875rem;
  font-weight: 500;
  transition: all 0.2s ease;
  border-left: 2px solid transparent;
}

.course-nav-link svg {
  flex-shrink: 0;
}

.course-nav-link:hover {
  background: rgba(255, 255, 255, 0.05);
  color: var(--color-text);
}

.course-nav-link.is-active {
  color: var(--color-accent);
  background: rgba(34, 211, 238, 0.05);
  border-left-color: var(--color-accent);
}

.breadcrumb {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--color-text-muted);
  margin-bottom: var(--space-md);
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.course-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-md);
  margin-top: var(--space-3xl);
  padding-top: var(--space-xl);
  border-top: 1px solid var(--color-border);
}

.course-nav a {
  flex: 1;
  background: rgba(255, 255, 255, 0.02);
  border: 1px solid var(--color-border);
  padding: var(--space-lg);
  border-radius: var(--radius-md);
  text-decoration: none;
  transition: all 0.2s ease;
}

.course-nav a:hover {
  background: rgba(255, 255, 255, 0.05);
  border-color: var(--color-accent);
}

.course-nav .label {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--color-text-muted);
  text-transform: uppercase;
  margin-bottom: var(--space-xs);
}

/* ==========================================================================
   Empty state
   ========================================================================== */

.empty-state {
  padding: var(--space-xl);
  border: 1px dashed var(--color-border);
  color: var(--color-text-muted);
  text-align: center;
}

.empty-state p {
  margin: 0;
}

/* ==========================================================================
   Responsive
   ========================================================================== */

@media (max-width: 768px) {
  .site-shell {
    padding: 0 var(--space-md);
  }

  .site-main {
    padding: var(--space-xl) 0 var(--space-2xl);
  }

  h1 {
    font-size: 1.625rem;
  }

  h2 {
    font-size: 1.3125rem;
  }

  /* Mobile nav */
  .nav-toggle-label {
    display: block;
  }

  .site-header nav {
    display: none;
    width: 100%;
    order: 3;
    padding-top: var(--space-sm);
    border-top: 1px solid var(--color-border-light);
  }

  .nav-toggle:checked~nav {
    display: block;
  }

  .site-header nav ul {
    flex-direction: column;
    gap: 0;
  }

  .site-header nav a {
    display: block;
    padding: var(--space-sm) 0;
    border-bottom: none;
  }

  .site-header nav a.is-active {
    border-bottom: none;
    color: var(--color-accent);
  }

  .site-header {
    flex-wrap: wrap;
  }

  /* Course: collapse sidebar */
  .course-layout {
    grid-template-columns: 1fr;
    gap: 0;
  }

  .course-sidebar {
    position: static;
    margin-bottom: var(--space-xl);
    border-bottom: 1px solid var(--color-border-light);
    padding-bottom: var(--space-md);
  }

  .course-sidebar-label {
    display: flex;
    align-items: center;
    justify-content: space-between;
    cursor: pointer;
    padding: var(--space-sm) 0;
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--color-text);
  }

  .course-sidebar-label::after {
    content: "▾";
    font-size: 0.75rem;
    color: var(--color-text-muted);
  }

  .course-sidebar nav {
    display: none;
    padding-top: var(--space-sm);
  }

  .course-sidebar-toggle:checked~nav {
    display: block;
  }

  .course-sidebar-toggle:checked~.course-sidebar-label::after {
    content: "▴";
  }

  /* Course nav stacks on mobile */
  .course-nav {
    flex-direction: column;
  }

  .course-nav a {
    max-width: 100%;
  }

  .course-nav .next {
    text-align: left;
    margin-left: 0;
  }

  .section-heading {
    flex-direction: column;
    align-items: flex-start;
  }
}

@media (max-width: 480px) {
  h1 {
    font-size: 1.375rem;
  }
}

/* ==========================================================================
   Search Overlay
   ========================================================================== */

.search-overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.5);
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding: 10vh var(--space-md);
  z-index: 1000;
  backdrop-filter: blur(4px);
}

.search-overlay.is-visible {
  display: flex;
}

.search-modal {
  background: var(--color-bg);
  width: 100%;
  max-width: 600px;
  border-radius: 8px;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
  overflow: hidden;
  border: 1px solid var(--color-border);
}

#search-input {
  width: 100%;
  padding: var(--space-md) var(--space-lg);
  border: none;
  border-bottom: 1px solid var(--color-border-light);
  font-size: 1.125rem;
  font-family: var(--font-body);
  outline: none;
}

.search-results {
  list-style: none;
  margin: 0;
  padding: 0;
  max-height: 60vh;
  overflow-y: auto;
}

.search-results li a {
  display: block;
  padding: var(--space-md) var(--space-lg);
  text-decoration: none;
  color: var(--color-text);
  border-bottom: 1px solid var(--color-border-light);
  transition: background 0.15s ease;
}

.search-results li:last-child a {
  border-bottom: none;
}

.search-results li a:hover {
  background: var(--color-bg-subtle);
}

.search-result-title {
  display: block;
  font-weight: 600;
  margin-bottom: 0.25rem;
}

.search-result-section {
  font-size: 0.75rem;
  text-transform: uppercase;
  color: var(--color-text-muted);
  letter-spacing: 0.05em;
  margin-bottom: 0.25rem;
  display: block;
}

.search-result-snippet {
  font-size: 0.875rem;
  color: var(--color-text-secondary);
  line-height: 1.4;
}

.search-no-results {
  padding: var(--space-lg);
  text-align: center;
  color: var(--color-text-muted);
}

/* ==========================================================================
   Accessibility
   ========================================================================== */

@media (prefers-reduced-motion: reduce) {

  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
  }
}