/* ============================================
   AI 进化之旅 — Design System & Global Styles
   ============================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800;900&family=Noto+Sans+SC:wght@300;400;500;600;700;900&family=JetBrains+Mono:wght@400;500;600&display=swap');

/* --- CSS Custom Properties --- */
:root {
  /* Colors */
  --c-bg-primary: #0a0a1a;
  --c-bg-secondary: #12122a;
  --c-bg-card: rgba(255, 255, 255, 0.04);
  --c-bg-card-hover: rgba(255, 255, 255, 0.08);
  --c-bg-glass: rgba(255, 255, 255, 0.06);
  --c-border: rgba(255, 255, 255, 0.08);
  --c-border-hover: rgba(255, 255, 255, 0.15);

  --c-text-primary: #e8e8f0;
  --c-text-secondary: rgba(232, 232, 240, 0.6);
  --c-text-muted: rgba(232, 232, 240, 0.35);

  --c-accent-purple: #6C5CE7;
  --c-accent-cyan: #00D2FF;
  --c-accent-red: #FF6B6B;
  --c-accent-green: #2ED573;
  --c-accent-orange: #FFA502;
  --c-accent-pink: #FD79A8;

  --g-primary: linear-gradient(135deg, #6C5CE7, #00D2FF);
  --g-warm: linear-gradient(135deg, #FF6B6B, #FFA502);
  --g-cool: linear-gradient(135deg, #00D2FF, #2ED573);
  --g-hero: linear-gradient(160deg, #0a0a1a 0%, #1a1040 40%, #0a2040 70%, #0a0a1a 100%);

  /* Typography */
  --f-sans: 'Inter', 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
  --f-mono: 'JetBrains Mono', 'Fira Code', monospace;

  --fs-xs: 0.75rem;
  --fs-sm: 0.875rem;
  --fs-base: 1rem;
  --fs-lg: 1.125rem;
  --fs-xl: 1.25rem;
  --fs-2xl: 1.5rem;
  --fs-3xl: 2rem;
  --fs-4xl: 2.5rem;
  --fs-5xl: 3.5rem;
  --fs-hero: clamp(2.5rem, 6vw, 5rem);

  /* Spacing */
  --s-xs: 0.25rem;
  --s-sm: 0.5rem;
  --s-md: 1rem;
  --s-lg: 1.5rem;
  --s-xl: 2rem;
  --s-2xl: 3rem;
  --s-3xl: 4rem;
  --s-4xl: 6rem;

  /* Border Radius */
  --r-sm: 8px;
  --r-md: 12px;
  --r-lg: 16px;
  --r-xl: 24px;
  --r-full: 9999px;

  /* Shadows */
  --shadow-sm: 0 2px 8px rgba(0,0,0,0.3);
  --shadow-md: 0 4px 16px rgba(0,0,0,0.4);
  --shadow-lg: 0 8px 32px rgba(0,0,0,0.5);
  --shadow-glow-purple: 0 0 30px rgba(108, 92, 231, 0.3);
  --shadow-glow-cyan: 0 0 30px rgba(0, 210, 255, 0.3);

  /* Transitions */
  --ease-out: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-bounce: cubic-bezier(0.68, -0.55, 0.265, 1.55);
  --t-fast: 150ms;
  --t-normal: 300ms;
  --t-slow: 500ms;
}

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

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

body {
  font-family: var(--f-sans);
  background: var(--c-bg-primary);
  color: var(--c-text-primary);
  line-height: 1.7;
  overflow-x: hidden;
  min-height: 100vh;
}

a {
  color: var(--c-accent-cyan);
  text-decoration: none;
  transition: color var(--t-fast) var(--ease-out);
}
a:hover { color: var(--c-accent-purple); }

img { max-width: 100%; display: block; }

button {
  font-family: var(--f-sans);
  cursor: pointer;
  border: none;
  outline: none;
  background: none;
  color: inherit;
}

/* --- Scrollbar --- */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: var(--c-bg-primary); }
::-webkit-scrollbar-thumb {
  background: rgba(108, 92, 231, 0.4);
  border-radius: var(--r-full);
}
::-webkit-scrollbar-thumb:hover { background: rgba(108, 92, 231, 0.6); }

/* --- Utility Classes --- */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 var(--s-xl);
}

.gradient-text {
  background: var(--g-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.glass {
  background: var(--c-bg-glass);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border: 1px solid var(--c-border);
}

.glow-purple { box-shadow: var(--shadow-glow-purple); }
.glow-cyan { box-shadow: var(--shadow-glow-cyan); }

/* --- Navigation --- */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 1000;
  padding: var(--s-md) 0;
  transition: all var(--t-normal) var(--ease-out);
}

.nav.scrolled {
  background: rgba(10, 10, 26, 0.9);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--c-border);
}

.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.nav-logo {
  font-size: var(--fs-lg);
  font-weight: 700;
  display: flex;
  align-items: center;
  gap: var(--s-sm);
}

.nav-logo .logo-icon {
  width: 32px;
  height: 32px;
  background: var(--g-primary);
  border-radius: var(--r-sm);
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
}

.nav-progress {
  display: flex;
  align-items: center;
  gap: var(--s-sm);
}

.nav-progress-bar {
  width: 200px;
  height: 4px;
  background: var(--c-bg-card);
  border-radius: var(--r-full);
  overflow: hidden;
}

.nav-progress-fill {
  height: 100%;
  background: var(--g-primary);
  border-radius: var(--r-full);
  transition: width var(--t-slow) var(--ease-out);
  width: 0%;
}

.nav-progress-text {
  font-size: var(--fs-xs);
  color: var(--c-text-muted);
  font-family: var(--f-mono);
  min-width: 35px;
}

.nav-chapters {
  display: flex;
  gap: var(--s-xs);
}

.nav-dot {
  width: 10px;
  height: 10px;
  border-radius: 50%;
  background: var(--c-bg-card);
  border: 1.5px solid var(--c-border);
  transition: all var(--t-normal) var(--ease-out);
  cursor: pointer;
  position: relative;
}

.nav-dot:hover {
  border-color: var(--c-accent-cyan);
  transform: scale(1.3);
}

.nav-dot.active {
  background: var(--c-accent-purple);
  border-color: var(--c-accent-purple);
  box-shadow: 0 0 10px rgba(108, 92, 231, 0.5);
}

.nav-dot.completed {
  background: var(--c-accent-green);
  border-color: var(--c-accent-green);
}

.nav-dot .tooltip {
  position: absolute;
  top: calc(100% + 8px);
  left: 50%;
  transform: translateX(-50%);
  background: var(--c-bg-secondary);
  color: var(--c-text-primary);
  padding: var(--s-xs) var(--s-sm);
  border-radius: var(--r-sm);
  font-size: var(--fs-xs);
  white-space: nowrap;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--t-fast) var(--ease-out);
  border: 1px solid var(--c-border);
}

.nav-dot:hover .tooltip { opacity: 1; }

/* --- Chapters --- */
.chapter {
  min-height: 100vh;
  padding: var(--s-4xl) 0;
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.chapter-header {
  text-align: center;
  margin-bottom: var(--s-3xl);
}

.chapter-number {
  font-size: var(--fs-sm);
  font-family: var(--f-mono);
  color: var(--c-accent-purple);
  letter-spacing: 3px;
  text-transform: uppercase;
  margin-bottom: var(--s-md);
  display: block;
}

.chapter-title {
  font-size: var(--fs-4xl);
  font-weight: 800;
  line-height: 1.2;
  margin-bottom: var(--s-lg);
}

.chapter-subtitle {
  font-size: var(--fs-lg);
  color: var(--c-text-secondary);
  max-width: 600px;
  margin: 0 auto;
}

/* --- Hero Section --- */
.hero {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  background: var(--g-hero);
  position: relative;
  overflow: hidden;
}

.hero-content {
  position: relative;
  z-index: 2;
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--s-sm);
  padding: var(--s-sm) var(--s-lg);
  border-radius: var(--r-full);
  font-size: var(--fs-sm);
  color: var(--c-accent-cyan);
  margin-bottom: var(--s-xl);
  background: rgba(0, 210, 255, 0.08);
  border: 1px solid rgba(0, 210, 255, 0.2);
}

.hero-title {
  font-size: var(--fs-hero);
  font-weight: 900;
  line-height: 1.1;
  margin-bottom: var(--s-xl);
}

.hero-desc {
  font-size: var(--fs-xl);
  color: var(--c-text-secondary);
  max-width: 650px;
  margin: 0 auto var(--s-2xl);
  line-height: 1.8;
}

.hero-cta {
  display: inline-flex;
  align-items: center;
  gap: var(--s-sm);
  padding: var(--s-md) var(--s-2xl);
  background: var(--g-primary);
  color: white;
  font-size: var(--fs-lg);
  font-weight: 600;
  border-radius: var(--r-full);
  transition: all var(--t-normal) var(--ease-out);
  box-shadow: var(--shadow-glow-purple);
}

.hero-cta:hover {
  transform: translateY(-2px) scale(1.02);
  box-shadow: 0 0 50px rgba(108, 92, 231, 0.5);
  color: white;
}

.hero-cta .arrow {
  transition: transform var(--t-normal) var(--ease-out);
}
.hero-cta:hover .arrow { transform: translateX(4px); }

.hero-scroll-hint {
  position: absolute;
  bottom: var(--s-2xl);
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--s-sm);
  color: var(--c-text-muted);
  font-size: var(--fs-sm);
  animation: float 2s ease-in-out infinite;
}

@keyframes float {
  0%, 100% { transform: translateX(-50%) translateY(0); }
  50% { transform: translateX(-50%) translateY(-10px); }
}

/* --- Particle Background --- */
#particles-canvas {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  z-index: 0;
  pointer-events: none;
  opacity: 0.5;
}

/* --- Fade In Animation --- */
.fade-in {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.8s var(--ease-out), transform 0.8s var(--ease-out);
}

.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

.fade-in-left {
  opacity: 0;
  transform: translateX(-40px);
  transition: opacity 0.8s var(--ease-out), transform 0.8s var(--ease-out);
}

.fade-in-left.visible {
  opacity: 1;
  transform: translateX(0);
}

.fade-in-right {
  opacity: 0;
  transform: translateX(40px);
  transition: opacity 0.8s var(--ease-out), transform 0.8s var(--ease-out);
}

.fade-in-right.visible {
  opacity: 1;
  transform: translateX(0);
}

/* Stagger children */
.stagger-children .fade-in:nth-child(1) { transition-delay: 0s; }
.stagger-children .fade-in:nth-child(2) { transition-delay: 0.1s; }
.stagger-children .fade-in:nth-child(3) { transition-delay: 0.2s; }
.stagger-children .fade-in:nth-child(4) { transition-delay: 0.3s; }
.stagger-children .fade-in:nth-child(5) { transition-delay: 0.4s; }
.stagger-children .fade-in:nth-child(6) { transition-delay: 0.5s; }

/* --- Chapter Transition Divider --- */
.chapter-divider {
  height: 200px;
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
}

.chapter-divider::before {
  content: '';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 1px;
  height: 100px;
  background: linear-gradient(to bottom, transparent, var(--c-accent-purple), transparent);
}

.chapter-divider .divider-icon {
  width: 48px;
  height: 48px;
  background: var(--c-bg-secondary);
  border: 1px solid var(--c-border);
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 20px;
  z-index: 1;
}

/* --- Responsive --- */
@media (max-width: 768px) {
  :root {
    --fs-4xl: 2rem;
    --fs-3xl: 1.75rem;
  }

  .container { padding: 0 var(--s-md); }
  .chapter { padding: var(--s-2xl) 0; }
  .nav-progress-bar { width: 100px; }
  .nav-chapters { display: none; }
}