/* ========================================
   HR Vibe-Coder 学习网站 — v2 Design System
   Aesthetic: "Warm Editorial" — 教科书质感
   Typography: Noto Serif SC + LXGW WenKai
   ======================================== */

@import url('https://fonts.googleapis.com/css2?family=Noto+Serif+SC:wght@400;700;900&family=JetBrains+Mono:wght@400;600&display=swap');
@import url('https://cdn.jsdelivr.net/npm/lxgw-wenkai-webfont@1.7.0/style.css');

/* --- CSS Variables --- */
:root {
  /* Warm editorial palette */
  --bg-primary: #faf8f5;
  --bg-secondary: rgba(250,248,245,0.85);
  --bg-card: #ffffff;
  --bg-code: #1e1e2e;
  --bg-accent: #f5f0eb;
  --bg-hr-tip: linear-gradient(135deg, #fff8f0, #fff3e0);
  --bg-quiz: linear-gradient(135deg, #f0faf5, #e8f5e9);
  --bg-interactive: linear-gradient(135deg, #f5f0ff, #ede7f6);
  --text-primary: #2c1810;
  --text-secondary: #6b5b4f;
  --text-muted: #9e8e82;
  --border: #e8ddd4;
  --border-light: #f0e8e0;
  --accent: #c2410c;
  --accent-light: #fff7ed;
  --accent-hover: #9a3412;
  --accent-gradient: linear-gradient(135deg, #c2410c, #dc2626);
  --track-a: #1e40af;
  --track-a-bg: #dbeafe;
  --track-a-glow: rgba(30,64,175,0.08);
  --track-b: #7c3aed;
  --track-b-bg: #ede9fe;
  --track-b-glow: rgba(124,58,237,0.08);
  --success: #16a34a;
  --success-bg: #f0fdf4;
  --warning: #d97706;
  --warning-bg: #fffbeb;
  --danger: #dc2626;
  --danger-bg: #fef2f2;
  --info: #2563eb;
  --info-bg: #eff6ff;
  --shadow-sm: 0 1px 3px rgba(44,24,16,0.04), 0 1px 2px rgba(44,24,16,0.06);
  --shadow-md: 0 4px 16px rgba(44,24,16,0.06), 0 2px 6px rgba(44,24,16,0.04);
  --shadow-lg: 0 12px 40px rgba(44,24,16,0.08), 0 4px 12px rgba(44,24,16,0.04);
  --shadow-glow: 0 0 0 3px rgba(194,65,12,0.1);
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 18px;
  --radius-xl: 24px;
  --font-display: "Noto Serif SC", "Georgia", serif;
  --font-body: "LXGW WenKai", "Noto Sans SC", sans-serif;
  --font-mono: "JetBrains Mono", "SF Mono", monospace;
  --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  --transition-spring: 0.4s cubic-bezier(0.34, 1.56, 0.64, 1);
}

/* Dark theme */
[data-theme="dark"] {
  --bg-primary: #141210;
  --bg-secondary: rgba(20,18,16,0.85);
  --bg-card: #1c1a18;
  --bg-code: #0d0d14;
  --bg-accent: #1f1c18;
  --bg-hr-tip: linear-gradient(135deg, #1f1a10, #221a0a);
  --bg-quiz: linear-gradient(135deg, #0f1f18, #0a1a10);
  --bg-interactive: linear-gradient(135deg, #1a1428, #180f25);
  --text-primary: #f0e8e0;
  --text-secondary: #b0a498;
  --text-muted: #7a6e62;
  --border: #2e2822;
  --border-light: #252018;
  --accent: #f97316;
  --accent-light: #1f1505;
  --accent-hover: #fb923c;
  --accent-gradient: linear-gradient(135deg, #f97316, #ef4444);
  --track-a-bg: #172554;
  --track-a-glow: rgba(30,64,175,0.15);
  --track-b-bg: #2e1065;
  --track-b-glow: rgba(124,58,237,0.15);
  --shadow-sm: 0 1px 3px rgba(0,0,0,0.2);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.25);
  --shadow-lg: 0 12px 40px rgba(0,0,0,0.3);
}

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

html {
  font-size: 16px;
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  font-family: var(--font-body);
  background: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.8;
  min-height: 100vh;
  /* Subtle paper texture */
  background-image:
    radial-gradient(ellipse at 20% 50%, rgba(194,65,12,0.03) 0%, transparent 50%),
    radial-gradient(ellipse at 80% 20%, rgba(124,58,237,0.03) 0%, transparent 50%);
}

a { color: var(--accent); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--accent-hover); text-decoration: underline; text-underline-offset: 3px; }

img { max-width: 100%; height: auto; }
ul, ol { padding-left: 1.5rem; }
li { margin-bottom: 0.4rem; }

/* --- Typography --- */
h1, h2, h3, h4 {
  font-family: var(--font-display);
  line-height: 1.35;
  font-weight: 700;
  letter-spacing: -0.01em;
}

h1 {
  font-size: 2.2rem;
  margin-bottom: 1rem;
  font-weight: 900;
}

h2 {
  font-size: 1.55rem;
  margin: 2.5rem 0 1rem;
  position: relative;
  padding-bottom: 0.5rem;
}

h2::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 40px;
  height: 3px;
  background: var(--accent-gradient);
  border-radius: 2px;
}

h3 {
  font-size: 1.2rem;
  margin: 1.5rem 0 0.75rem;
}

p { margin-bottom: 1rem; }

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

/* --- Layout --- */
.container {
  max-width: 780px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem;
}

.container-wide {
  max-width: 1080px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem;
}

/* --- Reading Progress Bar --- */
.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 0%;
  height: 3px;
  background: var(--accent-gradient);
  z-index: 1000;
  transition: width 0.1s linear;
}

/* --- Header / Nav --- */
.site-header {
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border);
  padding: 0.85rem 1.5rem;
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(16px) saturate(1.5);
  -webkit-backdrop-filter: blur(16px) saturate(1.5);
}

.site-header .inner {
  max-width: 1080px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.site-header .logo {
  font-family: var(--font-display);
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  display: flex;
  align-items: center;
  gap: 0.5rem;
  text-decoration: none;
}

.site-header .logo:hover { text-decoration: none; }

.site-header nav {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

.site-header nav a {
  font-size: 0.82rem;
  color: var(--text-secondary);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-sm);
  transition: all var(--transition);
  text-decoration: none;
  font-weight: 500;
}

.site-header nav a:hover,
.site-header nav a.active {
  color: var(--accent);
  background: var(--accent-light);
  text-decoration: none;
}

/* Theme toggle */
.theme-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 0.35rem 0.55rem;
  cursor: pointer;
  font-size: 1rem;
  color: var(--text-muted);
  transition: all var(--transition);
  line-height: 1;
}
.theme-toggle:hover {
  border-color: var(--accent);
  color: var(--accent);
  box-shadow: var(--shadow-glow);
}

/* Mobile nav */
.mobile-menu-btn {
  display: none;
  background: none;
  border: none;
  font-size: 1.4rem;
  cursor: pointer;
  color: var(--text-primary);
  padding: 0.25rem;
}

/* --- Cards --- */
.card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  box-shadow: var(--shadow-sm);
  transition: all var(--transition);
  position: relative;
}

.card:hover {
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  border-color: var(--border-light);
}

/* Lesson card on homepage */
.lesson-card {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  padding: 1.15rem 1.25rem;
  cursor: pointer;
  text-decoration: none !important;
  color: inherit;
  overflow: hidden;
}

.lesson-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 4px;
  height: 100%;
  background: transparent;
  transition: all var(--transition);
  border-radius: var(--radius-lg) 0 0 var(--radius-lg);
}

.lesson-card:hover::before {
  background: var(--accent-gradient);
}

.lesson-card .lesson-number {
  width: 42px;
  height: 42px;
  border-radius: 12px;
  background: var(--accent-light);
  color: var(--accent);
  display: flex;
  align-items: center;
  justify-content: center;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: 0.95rem;
  flex-shrink: 0;
  transition: all var(--transition-spring);
}

.lesson-card:hover .lesson-number {
  transform: scale(1.08);
  box-shadow: var(--shadow-glow);
}

.lesson-card.completed .lesson-number {
  background: var(--success-bg);
  color: var(--success);
}

.lesson-card.completed::after {
  content: '\2713';
  position: absolute;
  top: 0.75rem;
  right: 0.75rem;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  background: var(--success);
  color: white;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 0.7rem;
  font-weight: 700;
}

.lesson-card .lesson-info h3 {
  margin: 0 0 0.2rem;
  font-size: 1rem;
  font-family: var(--font-display);
}

.lesson-card .lesson-info p {
  margin: 0;
  font-size: 0.82rem;
  color: var(--text-secondary);
  line-height: 1.5;
}

.lesson-card .lesson-badge {
  font-size: 0.7rem;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  font-weight: 600;
  white-space: nowrap;
  letter-spacing: 0.02em;
}

.badge-track-a { background: var(--track-a-bg); color: var(--track-a); }
.badge-track-b { background: var(--track-b-bg); color: var(--track-b); }

/* --- HR Analogy Tip --- */
.hr-tip {
  background: var(--bg-hr-tip);
  border-left: 4px solid var(--warning);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  padding: 1.25rem 1.5rem;
  margin: 1.75rem 0;
  position: relative;
  overflow: hidden;
}

.hr-tip::before {
  content: "HR \7C7B\6BD4";
  display: block;
  font-size: 0.7rem;
  font-weight: 700;
  color: var(--warning);
  text-transform: uppercase;
  letter-spacing: 0.1em;
  margin-bottom: 0.6rem;
  font-family: var(--font-mono);
}

.hr-tip::after {
  content: '\1F465';
  position: absolute;
  right: 1rem;
  top: 0.75rem;
  font-size: 1.8rem;
  opacity: 0.15;
}

.hr-tip p { margin: 0; font-size: 0.92rem; line-height: 1.7; }

/* --- Code Block --- */
.code-block {
  background: var(--bg-code);
  border: 1px solid rgba(255,255,255,0.08);
  border-radius: var(--radius-md);
  padding: 1.15rem 1.4rem;
  overflow-x: auto;
  margin: 1.25rem 0;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  line-height: 1.7;
  color: #cdd6f4;
  position: relative;
}

.code-block::before {
  content: '';
  position: absolute;
  top: 0.75rem;
  left: 0.75rem;
  width: 8px; height: 8px;
  border-radius: 50%;
  background: #f38ba8;
  box-shadow: 14px 0 0 #a6e3a1, 28px 0 0 #f9e2af;
}

/* Catppuccin-inspired syntax */
.code-block .kw { color: #cba6f7; }
.code-block .str { color: #a6e3a1; }
.code-block .cm { color: #6c7086; font-style: italic; }
.code-block .fn { color: #89b4fa; }
.code-block .num { color: #fab387; }
.code-block .op { color: #f38ba8; }
.code-block .tag { color: #f5c2e7; }
.code-block .attr { color: #f9e2af; }

/* Inline code */
code {
  font-family: var(--font-mono);
  font-size: 0.82em;
  background: var(--bg-accent);
  color: var(--accent);
  padding: 0.15em 0.45em;
  border-radius: 5px;
  border: 1px solid var(--border-light);
  font-weight: 600;
}

/* --- Quiz Section --- */
.quiz-section {
  background: var(--bg-quiz);
  border: 1px solid rgba(34,197,94,0.2);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  margin: 2rem 0;
  position: relative;
}

.quiz-section h3 {
  margin: 0 0 1rem;
  color: var(--success);
  font-size: 0.95rem;
  font-family: var(--font-mono);
  font-weight: 600;
  letter-spacing: 0.02em;
}

.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  background: var(--bg-card);
  border: 2px solid var(--border);
  border-radius: var(--radius-md);
  padding: 0.8rem 1.1rem;
  margin: 0.5rem 0;
  cursor: pointer;
  font-size: 0.88rem;
  transition: all var(--transition);
  font-family: var(--font-body);
  color: var(--text-primary);
  position: relative;
  overflow: hidden;
}

.quiz-option::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  height: 100%;
  width: 0;
  background: var(--accent-gradient);
  opacity: 0.08;
  transition: width var(--transition);
}

.quiz-option:hover {
  border-color: var(--accent);
  transform: translateX(4px);
}

.quiz-option:hover::before { width: 100%; }

.quiz-option.correct {
  border-color: var(--success);
  background: var(--success-bg);
  transform: none;
}

.quiz-option.correct::before { width: 100%; background: rgba(22,163,74,0.1); }

.quiz-option.wrong {
  border-color: var(--danger);
  background: var(--danger-bg);
  transform: none;
  animation: shake 0.4s ease;
}

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-6px); }
  75% { transform: translateX(6px); }
}

.quiz-feedback {
  margin-top: 0.75rem;
  padding: 0.85rem 1.1rem;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  display: none;
  animation: slideUp 0.3s ease;
}

@keyframes slideUp {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

.quiz-feedback.show { display: block; }
.quiz-feedback.correct { background: var(--success-bg); color: #166534; border-left: 3px solid var(--success); }
.quiz-feedback.wrong { background: var(--danger-bg); color: #991b1b; border-left: 3px solid var(--danger); }

[data-theme="dark"] .quiz-feedback.correct { color: #86efac; }
[data-theme="dark"] .quiz-feedback.wrong { color: #fca5a5; }

/* --- Interactive Section --- */
.interactive-section {
  background: var(--bg-interactive);
  border: 1px solid rgba(147,51,234,0.15);
  border-radius: var(--radius-lg);
  padding: 1.5rem;
  margin: 2rem 0;
}

.interactive-section h3 {
  margin: 0 0 1rem;
  color: var(--track-b);
  font-size: 0.95rem;
  font-family: var(--font-mono);
  font-weight: 600;
}

/* Drag & Drop */
.drag-container {
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
}

.drag-items, .drop-zones { flex: 1; min-width: 200px; }

.drag-item {
  background: var(--bg-card);
  border: 2px dashed var(--border);
  border-radius: var(--radius-sm);
  padding: 0.65rem 1rem;
  margin: 0.4rem 0;
  cursor: grab;
  font-size: 0.85rem;
  transition: all var(--transition);
  user-select: none;
}
.drag-item:hover { border-color: var(--accent); transform: translateX(4px); }
.drag-item:active { cursor: grabbing; transform: scale(0.97); }
.drag-item.dragging { opacity: 0.4; }

.drop-zone {
  background: var(--bg-card);
  border: 2px dashed var(--border);
  border-radius: var(--radius-sm);
  padding: 0.65rem 1rem;
  margin: 0.4rem 0;
  min-height: 2.5rem;
  transition: all var(--transition);
}
.drop-zone.over { border-color: var(--accent); background: var(--accent-light); transform: scale(1.02); }
.drop-zone.correct { border-color: var(--success); border-style: solid; background: var(--success-bg); }
.drop-zone.wrong { border-color: var(--danger); border-style: solid; background: var(--danger-bg); animation: shake 0.4s ease; }

/* --- Progress Bar --- */
.progress-bar {
  width: 100%;
  height: 8px;
  background: var(--border);
  border-radius: 999px;
  overflow: hidden;
  margin: 0.5rem 0;
  position: relative;
}

.progress-bar .fill {
  height: 100%;
  background: var(--accent-gradient);
  border-radius: 999px;
  transition: width 0.6s cubic-bezier(0.34, 1.56, 0.64, 1);
  position: relative;
}

.progress-bar .fill::after {
  content: '';
  position: absolute;
  right: 0;
  top: -1px;
  width: 10px; height: 10px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 8px rgba(194,65,12,0.4);
}

.progress-text {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-family: var(--font-mono);
}

/* --- Lesson Page Layout --- */
.lesson-header {
  margin-bottom: 2.5rem;
  padding-bottom: 1.5rem;
  border-bottom: 1px solid var(--border);
}

.lesson-header .breadcrumb {
  font-size: 0.78rem;
  color: var(--text-muted);
  margin-bottom: 0.5rem;
  font-family: var(--font-mono);
}

.lesson-header .breadcrumb a { color: var(--text-muted); text-decoration: none; }
.lesson-header .breadcrumb a:hover { color: var(--accent); }

.lesson-header h1 { font-size: 2rem; }

.lesson-header .lesson-meta {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-top: 0.75rem;
  font-size: 0.82rem;
  color: var(--text-muted);
}

/* Lesson objectives */
.lesson-objectives {
  background: var(--bg-accent);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0 2rem;
}

.lesson-objectives h3 {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--accent);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin: 0 0 0.75rem;
}

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

.lesson-objectives li {
  padding-left: 1.5rem;
  position: relative;
  font-size: 0.9rem;
  margin-bottom: 0.3rem;
}

.lesson-objectives li::before {
  content: '\2192';
  position: absolute;
  left: 0;
  color: var(--accent);
  font-weight: 700;
}

/* Lesson nav */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  gap: 1rem;
}

.lesson-nav a {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.7rem 1.15rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-md);
  font-size: 0.88rem;
  transition: all var(--transition);
  text-decoration: none;
  color: var(--text-primary);
  flex: 1;
  max-width: 280px;
}

.lesson-nav a:hover {
  border-color: var(--accent);
  background: var(--accent-light);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
  text-decoration: none;
}

.lesson-nav a:last-child { justify-content: flex-end; text-align: right; }

/* --- SVG Diagram --- */
.diagram {
  margin: 2rem 0;
  text-align: center;
  padding: 1rem;
  background: var(--bg-accent);
  border-radius: var(--radius-lg);
  border: 1px solid var(--border-light);
}

.diagram svg {
  max-width: 100%;
  height: auto;
}

.diagram svg text {
  font-family: var(--font-body);
  fill: var(--text-primary);
}

[data-theme="dark"] .diagram svg text { fill: var(--text-primary); }

/* --- Info boxes --- */
.info-box {
  padding: 1.1rem 1.35rem;
  border-radius: var(--radius-md);
  margin: 1.25rem 0;
  font-size: 0.9rem;
  position: relative;
}

.info-box.tip { background: var(--info-bg); border-left: 4px solid var(--info); }
.info-box.warning { background: var(--warning-bg); border-left: 4px solid var(--warning); }
.info-box.success { background: var(--success-bg); border-left: 4px solid var(--success); }

/* --- Buttons --- */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  padding: 0.65rem 1.4rem;
  border-radius: var(--radius-md);
  font-size: 0.9rem;
  font-weight: 600;
  cursor: pointer;
  transition: all var(--transition);
  border: none;
  font-family: var(--font-body);
  position: relative;
  overflow: hidden;
}

.btn-primary {
  background: var(--accent-gradient);
  color: white;
  box-shadow: 0 2px 8px rgba(194,65,12,0.25);
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 16px rgba(194,65,12,0.35);
}

.btn-primary:active { transform: translateY(0); }

.btn-primary.completed {
  background: var(--success);
  box-shadow: 0 2px 8px rgba(22,163,74,0.25);
}

.btn-outline {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-primary);
}

.btn-outline:hover {
  border-color: var(--accent);
  color: var(--accent);
}

/* --- Homepage Hero --- */
.hero {
  text-align: center;
  padding: 4rem 0 3rem;
  position: relative;
}

.hero::before {
  content: '';
  position: absolute;
  top: -50%;
  left: 50%;
  transform: translateX(-50%);
  width: 600px;
  height: 600px;
  background: radial-gradient(circle, rgba(194,65,12,0.06) 0%, transparent 70%);
  pointer-events: none;
}

.hero h1 {
  font-size: 2.8rem;
  margin-bottom: 0.75rem;
  font-weight: 900;
  background: var(--accent-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
  line-height: 1.2;
}

.hero .subtitle {
  font-size: 1.1rem;
  color: var(--text-secondary);
  max-width: 480px;
  margin: 0 auto 2.5rem;
  line-height: 1.7;
}

/* Track sections */
.track-section { margin: 2.5rem 0; }

.track-section .track-header {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.25rem;
}

.track-section .track-header h2 {
  margin: 0;
  font-size: 1.3rem;
}

.track-section .track-header h2::after { display: none; }

.track-icon {
  width: 36px;
  height: 36px;
  border-radius: 10px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.15rem;
}

.track-icon-a { background: var(--track-a-bg); }
.track-icon-b { background: var(--track-b-bg); }

.lessons-grid {
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

/* --- Scroll reveal animation --- */
.reveal {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

.reveal.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Stagger children */
.stagger > * {
  opacity: 0;
  transform: translateY(12px);
  animation: staggerIn 0.5s ease forwards;
}

@keyframes staggerIn {
  to { opacity: 1; transform: translateY(0); }
}

.stagger > *:nth-child(1) { animation-delay: 0.05s; }
.stagger > *:nth-child(2) { animation-delay: 0.1s; }
.stagger > *:nth-child(3) { animation-delay: 0.15s; }
.stagger > *:nth-child(4) { animation-delay: 0.2s; }
.stagger > *:nth-child(5) { animation-delay: 0.25s; }
.stagger > *:nth-child(6) { animation-delay: 0.3s; }
.stagger > *:nth-child(7) { animation-delay: 0.35s; }
.stagger > *:nth-child(8) { animation-delay: 0.4s; }
.stagger > *:nth-child(9) { animation-delay: 0.45s; }
.stagger > *:nth-child(10) { animation-delay: 0.5s; }

.fade-in { animation: staggerIn 0.5s ease forwards; }

/* --- Footer --- */
footer {
  text-align: center;
  padding: 2.5rem 1.5rem;
  color: var(--text-muted);
  font-size: 0.8rem;
  border-top: 1px solid var(--border);
  font-family: var(--font-mono);
}

/* --- Mobile Nav Toggle --- */
.mobile-nav-toggle {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
  flex-direction: column;
  gap: 4px;
}

.mobile-nav-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  background: var(--text-primary);
  border-radius: 2px;
  transition: all var(--transition);
}

/* --- Responsive --- */
@media (max-width: 768px) {
  html { font-size: 15px; }
  .hero h1 { font-size: 2rem; }
  .hero .subtitle { font-size: 1rem; }
  .container { padding: 1.5rem 1rem; }
  .drag-container { flex-direction: column; }

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

  .site-header nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--bg-card);
    border-bottom: 1px solid var(--border);
    padding: 0.75rem 1rem;
    flex-direction: column;
    gap: 0.25rem;
    box-shadow: var(--shadow-md);
  }

  .site-header nav.open { display: flex; }

  .site-header nav a {
    display: block;
    padding: 0.5rem 0.75rem;
  }

  .site-header .inner { position: relative; }

  .lesson-nav { flex-direction: column; }
  .lesson-nav a { max-width: 100%; }

  h2 { font-size: 1.3rem; }
}

@media (max-width: 480px) {
  .hero h1 { font-size: 1.7rem; }
  .lesson-card .lesson-badge { display: none; }
}

/* --- Scrollbar --- */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 999px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-muted); }

/* --- Selection --- */
::selection {
  background: rgba(194,65,12,0.15);
  color: var(--text-primary);
}