/* ===== CSS Custom Properties (Light/Dark Mode) ===== */
:root {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-card: #ffffff;
  --text-primary: #1e293b;
  --text-secondary: #475569;
  --text-muted: #94a3b8;
  --accent: #6366f1;
  --accent-hover: #4f46e5;
  --accent-light: #e0e7ff;
  --border: #e2e8f0;
  --border-light: #f1f5f9;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.08);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.08);
  --shadow-lg: 0 8px 24px rgba(0,0,0,0.1);
  --code-bg: #f1f5f9;
  --code-text: #16a34a;
  --link: #6366f1;
  --heading-bg: #6366f1;
  --heading-text: #ffffff;
  --success: #22c55e;
  --warning: #f59e0b;
  --danger: #ef4444;
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;
  --radius-xl: 24px;
  --nav-bg: #ffffff;
  --nav-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

[data-theme="dark"] {
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #1e293b;
  --bg-card: #1e293b;
  --text-primary: #e2e8f0;
  --text-secondary: #94a3b8;
  --text-muted: #64748b;
  --accent: #818cf8;
  --accent-hover: #6366f1;
  --accent-light: #1e1b4b;
  --border: #334155;
  --border-light: #1e293b;
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 12px rgba(0,0,0,0.3);
  --shadow-lg: 0 8px 24px rgba(0,0,0,0.4);
  --code-bg: #1e293b;
  --code-text: #4ade80;
  --link: #818cf8;
  --heading-bg: #4338ca;
  --heading-text: #e2e8f0;
  --success: #4ade80;
  --warning: #fbbf24;
  --danger: #f87171;
  --nav-bg: #1e293b;
  --nav-shadow: 0 1px 3px rgba(0,0,0,0.4);
}

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

/* ===== Base ===== */
html { scroll-behavior: smooth; }

body {
  font-family: 'Inter', 'Segoe UI', system-ui, -apple-system, sans-serif;
  font-size: 1rem;
  line-height: 1.7;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  transition: background-color 0.3s, color 0.3s;
  -webkit-font-smoothing: antialiased;
}

/* ===== Site Navigation ===== */
.site-nav {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: var(--nav-bg);
  box-shadow: var(--nav-shadow);
  border-bottom: 1px solid var(--border);
  transition: background 0.3s, box-shadow 0.3s;
}

.site-nav .nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0.5rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.site-nav .nav-brand {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--accent);
  text-decoration: none;
  white-space: nowrap;
}

.site-nav .nav-links {
  display: flex;
  align-items: center;
  gap: 0.25rem;
  flex-wrap: wrap;
  list-style: none;
}

.site-nav .nav-links a {
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.85rem;
  padding: 0.35rem 0.65rem;
  border-radius: var(--radius-sm);
  transition: color 0.2s, background 0.2s;
  white-space: nowrap;
}

.site-nav .nav-links a:hover,
.site-nav .nav-links a.active {
  color: var(--accent);
  background: var(--accent-light);
}

/* Theme Toggle */
.theme-toggle {
  background: none;
  border: 2px solid var(--border);
  color: var(--text-secondary);
  width: 38px;
  height: 38px;
  border-radius: 50%;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.15rem;
  transition: border-color 0.2s, color 0.2s, background 0.2s;
  flex-shrink: 0;
}

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

/* Mobile nav hamburger */
.nav-toggle {
  display: none;
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  cursor: pointer;
  padding: 0.25rem;
}

@media (max-width: 768px) {
  .nav-toggle { display: block; }
  .site-nav .nav-links {
    display: none;
    width: 100%;
    flex-direction: column;
    padding: 0.5rem 0;
  }
  .site-nav .nav-links.open { display: flex; }
  .site-nav .nav-links a {
    width: 100%;
    padding: 0.6rem 0.75rem;
  }
  .site-nav .nav-inner { flex-wrap: wrap; }
  .nav-right { display: flex; align-items: center; gap: 0.5rem; }
}

@media (min-width: 769px) {
  .nav-right { display: flex; align-items: center; gap: 0.5rem; }
}

/* ===== Typography ===== */
h1, h2, h3, h4, h5, h6 { font-weight: 700; line-height: 1.3; }

h1 {
  font-size: clamp(1.75rem, 4vw, 2.5rem);
  background: var(--heading-bg);
  color: var(--heading-text);
  padding: 1rem 1.5rem;
  margin: 0 0 1rem;
  border-radius: var(--radius-md);
  text-align: center;
}

h2 {
  font-size: clamp(1.35rem, 3vw, 1.75rem);
  background: var(--heading-bg);
  color: var(--heading-text);
  padding: 0.75rem 1.25rem;
  margin: 2rem 0 1rem;
  border-radius: var(--radius-sm);
}

h3 {
  font-size: clamp(1.1rem, 2.5vw, 1.35rem);
  color: var(--text-primary);
  background: none;
  padding: 0.5rem 0;
  margin: 1.25rem 0 0.5rem;
}

h4 {
  font-size: 1.1rem;
  color: var(--text-primary);
  background: none;
  padding: 0.25rem 0;
  margin: 1rem 0 0.35rem;
}

strong { font-weight: 700; color: var(--text-primary); }
em { font-style: italic; }

p {
  margin: 0.75rem 0;
  color: var(--text-secondary);
}

a { color: var(--link); transition: color 0.2s; }
a:hover { color: var(--accent-hover); }

/* ===== Main Content Wrapper ===== */
main {
  max-width: 960px;
  margin: 0 auto;
  padding: 1.5rem;
}

header {
  max-width: 960px;
  margin: 0 auto;
  padding: 1.5rem 1.5rem 0;
}

header .subtitle {
  text-align: center;
  font-size: 1.1rem;
  color: var(--text-muted);
  margin-top: 0.5rem;
}

section { margin-bottom: 2rem; }

/* ===== Lists ===== */
ul, ol {
  margin: 0.5rem 0 0.5rem 1.5rem;
  color: var(--text-secondary);
}

ul { list-style-type: disc; }
ol { list-style-type: decimal; }

li {
  padding: 0.25rem 0;
  margin-left: 0;
}

ul li ul { margin-left: 1rem; }

/* ===== Code ===== */
code, pre {
  font-family: 'JetBrains Mono', 'Fira Code', 'Consolas', monospace;
  font-size: 0.9em;
}

code {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 0.15em 0.4em;
  border-radius: 4px;
}

pre {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 1rem;
  border-radius: var(--radius-md);
  overflow-x: auto;
  line-height: 1.6;
  margin: 1rem 0;
  border: 1px solid var(--border);
}

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

/* ===== Tables ===== */
table {
  width: 100%;
  max-width: 100%;
  border-collapse: collapse;
  margin: 1rem auto;
  font-size: 0.95rem;
  overflow-x: auto;
  display: block;
}

@media (min-width: 600px) {
  table { display: table; }
}

th, td {
  border: 1px solid var(--border);
  padding: 0.6rem 0.8rem;
  text-align: left;
  color: var(--text-secondary);
}

th {
  background: var(--bg-tertiary);
  font-weight: 700;
  color: var(--text-primary);
}

/* ===== Blockquote ===== */
blockquote {
  border-left: 4px solid var(--accent);
  background: var(--bg-tertiary);
  padding: 1rem 1.25rem;
  margin: 1rem 0;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: var(--text-secondary);
}

/* ===== Images ===== */
img {
  max-width: 100%;
  height: auto;
  border-radius: var(--radius-md);
  background: var(--bg-secondary);
}

/* ===== Canvas ===== */
canvas {
  max-width: 100%;
  height: auto;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
}

.canvas-container { text-align: center; margin: 1.5rem 0; }

/* ===== SVG ===== */
svg {
  display: block;
  margin: 0 auto;
  max-width: 100%;
}

/* ===== Mermaid ===== */
.mermaid, .mermaid_container, .mermaid-diagram {
  margin: 1.5rem auto;
  padding: 1.25rem;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  max-width: 100%;
  text-align: center;
  overflow-x: auto;
}

.mermaid svg { margin: 0 auto; display: block; }

/* ===== Footer ===== */
footer {
  max-width: 960px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
  text-align: center;
  color: var(--text-muted);
  border-top: 1px solid var(--border);
}

/* ===== Prev/Next Navigation ===== */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  max-width: 960px;
  margin: 2rem auto;
  padding: 0 1.5rem;
  flex-wrap: wrap;
}

.lesson-nav a {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.65rem 1.25rem;
  background: var(--bg-card);
  color: var(--accent);
  text-decoration: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  font-weight: 600;
  font-size: 0.9rem;
  transition: all 0.2s;
  box-shadow: var(--shadow-sm);
}

.lesson-nav a:hover {
  background: var(--accent);
  color: #fff;
  border-color: var(--accent);
  box-shadow: var(--shadow-md);
}

.lesson-nav .nav-next { margin-left: auto; }
.lesson-nav .nav-home { margin: 0 auto; }

@media (max-width: 500px) {
  .lesson-nav { flex-direction: column; align-items: stretch; }
  .lesson-nav a { justify-content: center; text-align: center; }
  .lesson-nav .nav-next { margin-left: 0; }
  .lesson-nav .nav-home { margin: 0; }
}

/* ===== Utility ===== */
.center { text-align: center; }
sup { font-size: 0.75em; vertical-align: super; }
sub { font-size: 0.75em; vertical-align: sub; }

/* ===== Dark mode overrides for inline page styles ===== */
[data-theme="dark"] .pronunciation-box,
[data-theme="dark"] .sentence-builder,
[data-theme="dark"] .cultural-note,
[data-theme="dark"] .cultural-immersion,
[data-theme="dark"] .exercise-box,
[data-theme="dark"] .pattern-demo,
[data-theme="dark"] .vocab-card,
[data-theme="dark"] .example-phrase,
[data-theme="dark"] .audio-tip,
[data-theme="dark"] .vocabulary-grid .vocab-card,
[data-theme="dark"] .vocabulary-section,
[data-theme="dark"] .particle-guide,
[data-theme="dark"] .focus-system,
[data-theme="dark"] .verb-conjugation,
[data-theme="dark"] .transformation-demo,
[data-theme="dark"] .morphology-tree,
[data-theme="dark"] .exercise-advanced,
[data-theme="dark"] .expression-box,
[data-theme="dark"] .idiom-card,
[data-theme="dark"] .proverb-showcase,
[data-theme="dark"] .cultural-expression,
[data-theme="dark"] .search-box,
[data-theme="dark"] .politeness-level,
[data-theme="dark"] .phrase-pattern,
[data-theme="dark"] .cultural-tip,
[data-theme="dark"] .dialogue-practice,
[data-theme="dark"] .exercise-interactive,
[data-theme="dark"] .conversation-box,
[data-theme="dark"] .speaker-a,
[data-theme="dark"] .speaker-b,
[data-theme="dark"] .festival-section,
[data-theme="dark"] .mastery-level,
[data-theme="dark"] .skill-meter,
[data-theme="dark"] .stat-card,
[data-theme="dark"] .interactive-quiz,
[data-theme="dark"] .quiz-question,
[data-theme="dark"] .quiz-option,
[data-theme="dark"] .dialogue-flow,
[data-theme="dark"] .grammar-box,
[data-theme="dark"] .conversation-showcase {
  background-color: var(--bg-secondary) !important;
  color: var(--text-primary) !important;
  border-color: var(--border) !important;
}

[data-theme="dark"] .lesson-card,
[data-theme="dark"] .feature-card,
[data-theme="dark"] .stat-card {
  background: var(--bg-card) !important;
  color: var(--text-primary) !important;
  border-color: var(--border) !important;
}

[data-theme="dark"] .lesson-title,
[data-theme="dark"] .lesson-description,
[data-theme="dark"] .lesson-highlights li,
[data-theme="dark"] .stat-number,
[data-theme="dark"] .feature-card h3,
[data-theme="dark"] .feature-card p {
  color: var(--text-primary) !important;
}

[data-theme="dark"] .lesson-highlights {
  background: var(--bg-tertiary) !important;
  border-color: var(--success) !important;
}

[data-theme="dark"] .stats-section,
[data-theme="dark"] .learning-path {
  background: var(--bg-secondary) !important;
}

[data-theme="dark"] .hero-section {
  background: linear-gradient(135deg, #4338ca 0%, #6d28d9 100%) !important;
}

[data-theme="dark"] .quick-start {
  background: linear-gradient(135deg, #b91c1c 0%, #ca8a04 100%) !important;
}

[data-theme="dark"] .footer-section {
  background: var(--bg-secondary) !important;
}

[data-theme="dark"] .difficulty-badge.beginner { background: #064e3b; color: #6ee7b7; }
[data-theme="dark"] .difficulty-badge.intermediate { background: #78350f; color: #fde68a; }
[data-theme="dark"] .difficulty-badge.advanced { background: #7f1d1d; color: #fca5a5; }
[data-theme="dark"] .difficulty-badge.mastery { background: #374151; color: #d1d5db; }

[data-theme="dark"] .quiz-option.correct { background: #064e3b !important; color: #6ee7b7 !important; }
[data-theme="dark"] .quiz-option.incorrect { background: #7f1d1d !important; color: #fca5a5 !important; }

[data-theme="dark"] canvas { border-color: var(--border) !important; }

/* ===== Print ===== */
@media print {
  .site-nav, .theme-toggle, .lesson-nav, .nav-toggle { display: none !important; }
  body { background: #fff; color: #000; }
}

/* BEGIN footer-nav-styles (managed by add_footer_nav.py) */
/* Static lesson footer (inserted by add_footer_nav.py into each lesson HTML) */
.site-footer {
    text-align: center;
    padding: 1.5rem 1rem;
    font-size: .85rem;
    color: var(--text-muted);
    border-top: 1px solid var(--border);
    margin-top: 2rem;
    max-width: 960px;
    margin-left: auto;
    margin-right: auto;
}
.site-footer a { color: var(--accent); text-decoration: none; }
.site-footer a:hover { text-decoration: underline; }
.site-footer p { margin: .35rem 0; }

.footer-links {
    display: flex;
    justify-content: center;
    gap: 1rem;
    flex-wrap: wrap;
    margin-top: .5rem;
}

/* Home-link: outlined "ghost" variant to distinguish from prev/next */
.lesson-nav .home-link {
    background: transparent;
    color: var(--accent);
    border: 2px solid var(--accent);
}
.lesson-nav .home-link:hover {
    background: var(--accent);
    color: #fff;
    border-color: var(--accent);
}

/* First lesson uses <span></span> as a prev placeholder; keep it inert */
.lesson-nav > span:empty { flex: 0 0 auto; }

@media print {
    .site-footer { display: none !important; }
}
/* END footer-nav-styles */