/**
 * 尘渊文化 - 核心样式系统 v4.0
 * 整合 design-system.css + main.css + components.css + navigation.css
 * 移除冗余，统一变量，优化性能
 */

/* ============================================================
   1. 设计变量
   ============================================================ */
:root {
  /* 品牌色 */
  --brand-50: #eef2ff;
  --brand-100: #e0e7ff;
  --brand-200: #c7d2fe;
  --brand-300: #a5b4fc;
  --brand-400: #818cf8;
  --brand-500: #6366f1;
  --brand-600: #4f46e5;
  --brand-700: #4338ca;
  --brand-800: #3730a3;
  --brand-900: #312e81;

  /* 强调色 */
  --accent-cyan: #22d3ee;
  --accent-pink: #ec4899;
  --accent-green: #10b981;
  --accent-amber: #f59e0b;
  --accent-red: #ef4444;

  /* 背景色 */
  --bg-base: #000000;
  --bg-surface: #0a0a0b;
  --bg-elevated: #141416;
  --bg-overlay: #1c1c1f;
  --bg-subtle: #27272a;
  --bg-light: #fafafa;

  /* 文字色 */
  --text-primary: #fafafa;
  --text-secondary: #a1a1aa;
  --text-tertiary: #71717a;
  --text-muted: #52525b;
  --text-brand: #a5b4fc;

  /* 边框 */
  --border-subtle: rgba(255, 255, 255, 0.06);
  --border-default: rgba(255, 255, 255, 0.1);
  --border-hover: rgba(255, 255, 255, 0.15);
  --border-brand: rgba(99, 102, 241, 0.5);

  /* 渐变 */
  --gradient-brand: linear-gradient(135deg, #6366f1 0%, #8b5cf6 50%, #ec4899 100%);
  --gradient-subtle: linear-gradient(180deg, rgba(99, 102, 241, 0.08) 0%, transparent 100%);
  --gradient-glow: radial-gradient(ellipse 80% 50% at 50% -20%, rgba(99, 102, 241, 0.15), transparent);
  --gradient-mesh: 
    radial-gradient(at 40% 20%, rgba(99, 102, 241, 0.08) 0px, transparent 50%),
    radial-gradient(at 80% 0%, rgba(139, 92, 246, 0.06) 0px, transparent 50%),
    radial-gradient(at 0% 50%, rgba(236, 72, 153, 0.04) 0px, transparent 50%);

  /* 阴影 */
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.3);
  --shadow-xl: 0 16px 48px rgba(0, 0, 0, 0.4);
  --shadow-glow: 0 0 40px rgba(99, 102, 241, 0.15);
  --shadow-brand: 0 0 24px rgba(99, 102, 241, 0.25);

  /* 圆角 */
  --radius-xs: 4px;
  --radius-sm: 6px;
  --radius-md: 8px;
  --radius-lg: 12px;
  --radius-xl: 16px;
  --radius-2xl: 24px;
  --radius-full: 9999px;

  /* 间距 */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 20px;
  --space-6: 24px;
  --space-8: 32px;
  --space-10: 40px;
  --space-12: 48px;
  --space-16: 64px;
  --space-20: 80px;
  --space-24: 96px;

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

  /* 字号 */
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;
  --text-4xl: 2.25rem;
  --text-5xl: 3rem;
  --text-6xl: 3.75rem;

  /* 行高 */
  --leading-tight: 1.25;
  --leading-normal: 1.5;
  --leading-relaxed: 1.75;

  /* 动画 */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --ease-in-out: cubic-bezier(0.65, 0, 0.35, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);
  --duration-fast: 150ms;
  --duration-normal: 250ms;
  --duration-slow: 400ms;

  /* 布局 */
  --container-sm: 640px;
  --container-md: 768px;
  --container-lg: 1024px;
  --container-xl: 1280px;
  --container-2xl: 1440px;
  --header-height: 64px;
}

/* ============================================================
   2. 重置与基础
   ============================================================ */
*, *::before, *::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

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

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: var(--leading-normal);
  color: var(--text-primary);
  background: var(--bg-base);
  min-height: 100vh;
}

/* ============================================================
   3. 排版
   ============================================================ */
h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-display);
  font-weight: 600;
  line-height: var(--leading-tight);
  letter-spacing: -0.02em;
}

h1 { font-size: var(--text-5xl); font-weight: 700; }
h2 { font-size: var(--text-4xl); }
h3 { font-size: var(--text-2xl); }
h4 { font-size: var(--text-xl); }
h5 { font-size: var(--text-lg); }
h6 { font-size: var(--text-base); }

p {
  color: var(--text-secondary);
  line-height: var(--leading-relaxed);
}

a {
  color: var(--text-brand);
  text-decoration: none;
  transition: color var(--duration-fast) var(--ease-out);
}

a:hover {
  color: var(--brand-300);
}

/* ============================================================
   4. 容器
   ============================================================ */
.container {
  width: 100%;
  max-width: var(--container-xl);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.container-sm { max-width: var(--container-sm); }
.container-md { max-width: var(--container-md); }
.container-lg { max-width: var(--container-lg); }
.container-2xl { max-width: var(--container-2xl); }

/* ============================================================
   5. 导航栏
   ============================================================ */
.navbar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: rgba(0, 0, 0, 0.8);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-subtle);
  z-index: 1000;
  transition: all var(--duration-normal) var(--ease-out);
}

.navbar.scrolled {
  background: rgba(0, 0, 0, 0.95);
  border-bottom-color: var(--border-default);
}

.navbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: var(--container-xl);
  margin: 0 auto;
  padding: 0 var(--space-6);
}

.navbar-brand {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
  text-decoration: none;
  transition: opacity var(--duration-fast) var(--ease-out);
}

.navbar-brand:hover {
  opacity: 0.9;
  color: var(--text-primary);
}

.brand-icon {
  width: 32px;
  height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--gradient-brand);
  border-radius: var(--radius-md);
  font-size: var(--text-base);
  font-weight: 700;
  color: white;
}

.navbar-nav {
  display: flex;
  align-items: center;
  gap: var(--space-1);
  list-style: none;
  margin: 0;
  padding: 0;
}

.navbar-nav li a {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-out);
}

.navbar-nav li a:hover {
  color: var(--text-primary);
  background: var(--bg-subtle);
}

.navbar-nav li a.active {
  color: var(--text-primary);
  background: var(--bg-elevated);
}

.navbar-actions {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.navbar-toggle {
  display: none;
  width: 40px;
  height: 40px;
  padding: 0;
  background: transparent;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: background var(--duration-fast) var(--ease-out);
}

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

.navbar-toggle span {
  display: block;
  width: 20px;
  height: 2px;
  margin: 5px auto;
  background: var(--text-primary);
  border-radius: 1px;
  transition: all var(--duration-fast) var(--ease-out);
}

.navbar-toggle.active span:nth-child(1) {
  transform: rotate(45deg) translate(5px, 5px);
}

.navbar-toggle.active span:nth-child(2) {
  opacity: 0;
}

.navbar-toggle.active span:nth-child(3) {
  transform: rotate(-45deg) translate(5px, -5px);
}

@media (max-width: 768px) {
  .navbar-toggle {
    display: block;
  }

  .navbar-nav {
    position: fixed;
    top: var(--header-height);
    left: 0;
    right: 0;
    bottom: 0;
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-1);
    padding: var(--space-4);
    background: var(--bg-base);
    border-top: 1px solid var(--border-subtle);
    opacity: 0;
    visibility: hidden;
    transform: translateY(-10px);
    transition: all var(--duration-normal) var(--ease-out);
  }

  .navbar-nav.active {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
  }

  /* 移动菜单遮罩层 */
  body.menu-open::before {
    content: '';
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.6);
    z-index: 999;
    backdrop-filter: blur(4px);
  }

  .navbar-nav li a {
    padding: var(--space-4);
    font-size: var(--text-base);
    border-radius: var(--radius-lg);
  }

  .navbar-actions {
    display: none;
  }
}

/* 移动菜单打开时禁止背景滚动 */
body.menu-open {
  overflow: hidden;
}

/* ============================================================
   6. 按钮系统
   ============================================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-5);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  font-weight: 500;
  line-height: 1;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  transition: all var(--duration-normal) var(--ease-out);
  white-space: nowrap;
}

.btn-primary {
  background: var(--brand-500);
  color: white;
}

.btn-primary:hover {
  background: var(--brand-400);
  box-shadow: var(--shadow-brand);
  transform: translateY(-1px);
}

.btn-secondary {
  background: var(--bg-elevated);
  color: var(--text-primary);
  border: 1px solid var(--border-default);
}

.btn-secondary:hover {
  background: var(--bg-overlay);
  border-color: var(--border-hover);
}

.btn-ghost {
  background: transparent;
  color: var(--text-secondary);
}

.btn-ghost:hover {
  color: var(--text-primary);
  background: var(--bg-subtle);
}

.btn-gradient {
  background: var(--gradient-brand);
  color: white;
  border: none;
  box-shadow: 0 0 20px rgba(99, 102, 241, 0.3);
}

.btn-gradient:hover {
  box-shadow: 0 0 30px rgba(99, 102, 241, 0.5);
  transform: translateY(-2px);
}

.btn-lg {
  padding: var(--space-4) var(--space-8);
  font-size: var(--text-base);
  border-radius: var(--radius-lg);
}

.btn-sm {
  padding: var(--space-2) var(--space-3);
  font-size: var(--text-xs);
}

.btn-icon {
  width: 40px;
  height: 40px;
  padding: 0;
  border-radius: var(--radius-md);
}

/* ============================================================
   7. 卡片系统
   ============================================================ */
.card {
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  padding: var(--space-6);
  transition: all var(--duration-normal) var(--ease-out);
}

.card:hover {
  border-color: var(--border-default);
  box-shadow: var(--shadow-lg);
}

.card-interactive:hover {
  border-color: var(--border-brand);
  transform: translateY(-4px);
  box-shadow: var(--shadow-glow);
}

.card-header {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-4);
}

.card-icon {
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--gradient-brand);
  border-radius: var(--radius-lg);
  font-size: var(--text-xl);
  flex-shrink: 0;
}

.card-title {
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--text-primary);
}

.card-desc {
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  line-height: var(--leading-relaxed);
}

/* 特色卡片 */
.feature-card {
  position: relative;
  padding: var(--space-6);
  background: var(--bg-elevated);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-xl);
  transition: all var(--duration-normal) var(--ease-out);
  overflow: hidden;
}

.feature-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--brand-500), transparent);
  opacity: 0;
  transition: opacity var(--duration-normal) var(--ease-out);
}

.feature-card:hover {
  border-color: var(--border-default);
  transform: translateY(-4px);
  box-shadow: var(--shadow-lg);
}

.feature-card:hover::before {
  opacity: 1;
}

/* ============================================================
   8. 徽章/标签
   ============================================================ */
.badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: var(--space-1) var(--space-3);
  font-size: var(--text-xs);
  font-weight: 500;
  border-radius: var(--radius-full);
  background: var(--bg-subtle);
  color: var(--text-secondary);
  border: 1px solid var(--border-subtle);
}

.badge-brand {
  background: rgba(99, 102, 241, 0.15);
  color: var(--brand-300);
  border-color: rgba(99, 102, 241, 0.3);
}

.badge-success {
  background: rgba(16, 185, 129, 0.15);
  color: #34d399;
  border-color: rgba(16, 185, 129, 0.3);
}

.badge-warning {
  background: rgba(245, 158, 11, 0.15);
  color: #fbbf24;
  border-color: rgba(245, 158, 11, 0.3);
}

/* ============================================================
   9. Hero区域
   ============================================================ */
.hero {
  position: relative;
  min-height: 100vh;
  display: flex;
  align-items: center;
  padding: var(--space-24) 0;
  background: var(--bg-base);
  overflow: hidden;
}

.hero::before {
  content: '';
  position: absolute;
  inset: 0;
  background: var(--gradient-mesh);
  pointer-events: none;
}

.hero-content {
  position: relative;
  z-index: 1;
  max-width: 800px;
}

.hero-title {
  font-size: clamp(2.5rem, 8vw, 4.5rem);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.03em;
  background: linear-gradient(135deg, #fff 0%, #a5b4fc 50%, #c4b5fd 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.hero-subtitle {
  font-size: var(--text-xl);
  color: var(--text-secondary);
  margin-top: var(--space-6);
  max-width: 600px;
}

.hero-actions {
  display: flex;
  gap: var(--space-4);
  margin-top: var(--space-10);
}

.hero-badge {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-3) var(--space-5);
  background: rgba(99, 102, 241, 0.1);
  border: 1px solid rgba(99, 102, 241, 0.3);
  border-radius: var(--radius-full);
  color: var(--brand-300);
  font-size: var(--text-sm);
  font-weight: 600;
  margin-bottom: var(--space-6);
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

/* ============================================================
   10. Section区域
   ============================================================ */
.section {
  padding: var(--space-24) 0;
  position: relative;
}

.section-header {
  text-align: center;
  margin-bottom: var(--space-16);
}

.section-tag {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: var(--space-2) var(--space-4);
  font-size: var(--text-xs);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--brand-300);
  background: rgba(99, 102, 241, 0.1);
  border: 1px solid rgba(99, 102, 241, 0.2);
  border-radius: var(--radius-full);
  margin-bottom: var(--space-4);
}

.section-title {
  font-size: var(--text-4xl);
  font-weight: 700;
  margin-bottom: var(--space-4);
}

.section-desc {
  font-size: var(--text-lg);
  color: var(--text-tertiary);
  max-width: 600px;
  margin: 0 auto;
}

/* ============================================================
   11. 页脚
   ============================================================ */
.footer {
  background: var(--bg-surface);
  border-top: 1px solid var(--border-subtle);
  padding: var(--space-16) 0 var(--space-8);
}

.footer-grid {
  display: grid;
  grid-template-columns: 2fr repeat(3, 1fr);
  gap: var(--space-12);
  margin-bottom: var(--space-12);
}

.footer-brand {
  max-width: 280px;
}

.footer-column h4 {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--text-primary);
  margin-bottom: var(--space-4);
}

.footer-links {
  list-style: none;
  padding: 0;
  margin: 0;
}

.footer-links li {
  margin-bottom: var(--space-2);
}

.footer-links a {
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  text-decoration: none;
  transition: color var(--duration-fast) var(--ease-out);
}

.footer-links a:hover {
  color: var(--text-primary);
}

.footer-bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: var(--space-8);
  border-top: 1px solid var(--border-subtle);
}

.footer-copyright {
  font-size: var(--text-sm);
  color: var(--text-muted);
}

.footer-social {
  display: flex;
  gap: var(--space-4);
}

.footer-social a {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-tertiary);
  border-radius: var(--radius-md);
  transition: all var(--duration-fast) var(--ease-out);
}

.footer-social a:hover {
  color: var(--text-primary);
  background: var(--bg-subtle);
}

@media (max-width: 768px) {
  .footer-grid {
    grid-template-columns: 1fr 1fr;
    gap: var(--space-8);
  }

  .footer-brand {
    grid-column: 1 / -1;
    max-width: none;
  }

  .footer-bottom {
    flex-direction: column;
    gap: var(--space-4);
    text-align: center;
  }
}

/* ============================================================
   12. 输入框
   ============================================================ */
.input {
  width: 100%;
  padding: var(--space-3) var(--space-4);
  font-family: var(--font-sans);
  font-size: var(--text-sm);
  color: var(--text-primary);
  background: var(--bg-surface);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-md);
  outline: none;
  transition: all var(--duration-fast) var(--ease-out);
}

.input:focus {
  border-color: var(--brand-500);
  box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.15);
}

.input::placeholder {
  color: var(--text-muted);
}

/* ============================================================
   13. 网格系统
   ============================================================ */
.grid {
  display: grid;
  gap: var(--space-6);
}

.grid-cols-2 { grid-template-columns: repeat(2, 1fr); }
.grid-cols-3 { grid-template-columns: repeat(3, 1fr); }
.grid-cols-4 { grid-template-columns: repeat(4, 1fr); }

@media (max-width: 1024px) {
  .grid-cols-4 { grid-template-columns: repeat(2, 1fr); }
  .grid-cols-3 { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 640px) {
  .grid-cols-4, .grid-cols-3, .grid-cols-2 { 
    grid-template-columns: 1fr; 
  }
}

/* ============================================================
   14. 动画效果
   ============================================================ */
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@keyframes slideUp {
  from { 
    opacity: 0;
    transform: translateY(20px);
  }
  to { 
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes scaleIn {
  from { 
    opacity: 0;
    transform: scale(0.95);
  }
  to { 
    opacity: 1;
    transform: scale(1);
  }
}

@keyframes shimmer {
  0% { background-position: -200% 0; }
  100% { background-position: 200% 0; }
}

@keyframes pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; }
}

.animate-fade-in {
  animation: fadeIn var(--duration-normal) var(--ease-out);
}

.animate-slide-up {
  animation: slideUp var(--duration-slow) var(--ease-out);
}

.animate-scale-in {
  animation: scaleIn var(--duration-normal) var(--ease-spring);
}

/* 滚动动画 */
.scroll-reveal {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s var(--ease-out), transform 0.6s var(--ease-out);
}

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

[data-animate] {
  opacity: 0;
  transform: translateY(30px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}

[data-animate].animate-in {
  opacity: 1;
  transform: translateY(0);
}

/* ============================================================
   15. 返回顶部
   ============================================================ */
.back-to-top {
  position: fixed;
  bottom: var(--space-8);
  right: var(--space-8);
  width: 44px;
  height: 44px;
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--radius-full);
  color: var(--text-secondary);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(10px);
  transition: all var(--duration-normal) var(--ease-out);
  z-index: 100;
}

.back-to-top.visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.back-to-top:hover {
  background: var(--bg-overlay);
  border-color: var(--border-hover);
  color: var(--text-primary);
}

@media (max-width: 768px) {
  .back-to-top {
    bottom: var(--space-6);
    right: var(--space-6);
  }
}

/* ============================================================
   16. 代码块
   ============================================================ */
pre, code {
  font-family: var(--font-mono);
}

code {
  padding: var(--space-1) var(--space-2);
  font-size: var(--text-sm);
  background: var(--bg-subtle);
  border-radius: var(--radius-sm);
  color: var(--brand-300);
}

pre {
  padding: var(--space-5);
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  overflow-x: auto;
}

pre code {
  padding: 0;
  background: transparent;
  color: var(--text-secondary);
}

/* ============================================================
   17. 面包屑
   ============================================================ */
.breadcrumb {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  color: var(--text-tertiary);
  margin-bottom: var(--space-6);
}

.breadcrumb a {
  color: var(--text-tertiary);
  text-decoration: none;
  transition: color var(--duration-fast) var(--ease-out);
}

.breadcrumb a:hover {
  color: var(--text-primary);
}

.breadcrumb-separator {
  color: var(--text-muted);
}

.breadcrumb-current {
  color: var(--text-secondary);
}

/* ============================================================
   18. 分隔线
   ============================================================ */
.divider {
  height: 1px;
  background: var(--border-subtle);
  margin: var(--space-8) 0;
}

/* ============================================================
   19. 骨架屏
   ============================================================ */
.skeleton {
  background: linear-gradient(90deg, var(--bg-elevated) 25%, var(--bg-subtle) 50%, var(--bg-elevated) 75%);
  background-size: 200% 100%;
  animation: shimmer 1.5s infinite;
  border-radius: var(--radius-md);
}

.skeleton-text {
  height: 16px;
  margin-bottom: var(--space-2);
}

.skeleton-title {
  height: 24px;
  width: 60%;
  margin-bottom: var(--space-4);
}

.skeleton-avatar {
  width: 48px;
  height: 48px;
  border-radius: var(--radius-full);
}

/* ============================================================
   20. 工具类
   ============================================================ */
.text-center { text-align: center; }
.text-left { text-align: left; }
.text-right { text-align: right; }

.text-brand { color: var(--brand-400); }
.text-muted { color: var(--text-tertiary); }
.text-secondary { color: var(--text-secondary); }

.font-mono { font-family: var(--font-mono); }

.flex { display: flex; }
.flex-col { flex-direction: column; }
.items-center { align-items: center; }
.justify-center { justify-content: center; }
.justify-between { justify-content: space-between; }
.gap-2 { gap: var(--space-2); }
.gap-4 { gap: var(--space-4); }
.gap-6 { gap: var(--space-6); }
.gap-8 { gap: var(--space-8); }

.mt-4 { margin-top: var(--space-4); }
.mt-6 { margin-top: var(--space-6); }
.mt-8 { margin-top: var(--space-8); }
.mb-4 { margin-bottom: var(--space-4); }
.mb-6 { margin-bottom: var(--space-6); }
.mb-8 { margin-bottom: var(--space-8); }

.w-full { width: 100%; }
.max-w-prose { max-width: 65ch; }

/* ============================================================
   21. 响应式隐藏
   ============================================================ */
@media (max-width: 768px) {
  .hide-mobile { display: none; }
}

@media (min-width: 769px) {
  .hide-desktop { display: none; }
}

/* ============================================================
   22. 减少动画偏好
   ============================================================ */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms;
    animation-iteration-count: 1;
    transition-duration: 0.01ms;
    scroll-behavior: auto;
  }
  
  [data-animate] {
    opacity: 1;
    transform: none;
  }
  
  .scroll-reveal {
    opacity: 1;
    transform: none;
  }
}