:root {
    --primary: #4f46e5;
    --primary-light: #eef2ff;
    --primary-dark: #4338ca;
    --text: #1e293b;
    --text-secondary: #64748b;
    --text-light: #94a3b8;
    --border: #e2e8f0;
    --bg: #ffffff;
    --bg-alt: #f8fafc;
    --sidebar-bg: #1e293b;
    --sidebar-text: #cbd5e1;
    --sidebar-active-bg: rgba(79,70,229,.15);
    --shadow-sm: 0 1px 2px rgba(0,0,0,.05);
    --shadow: 0 1px 3px rgba(0,0,0,.1), 0 1px 2px rgba(0,0,0,.06);
    --shadow-lg: 0 10px 15px -3px rgba(0,0,0,.1), 0 4px 6px -4px rgba(0,0,0,.1);
    --radius: 12px;
    --radius-sm: 8px;
    --gradient: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
  }
  * { margin: 0; padding: 0; box-sizing: border-box; }
  html { scroll-behavior: smooth; }
  body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
    color: var(--text);
    line-height: 1.7;
    background: #f1f5f9;
    display: flex;
    min-height: 100vh;
  }

  .mobile-topbar,
  .sidebar-overlay {
    display: none;
  }

  .mobile-topbar {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    height: 56px;
    padding: 0 16px;
    background: rgba(255, 255, 255, 0.96);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid rgba(226, 232, 240, 0.9);
    z-index: 30;
    align-items: center;
    justify-content: space-between;
  }

  .mobile-topbar-title {
    font-size: 15px;
    font-weight: 700;
    color: var(--text);
  }

  .mobile-topbar-spacer {
    width: 40px;
    height: 40px;
  }

  .mobile-nav-button {
    width: 40px;
    height: 40px;
    border: 1px solid var(--border);
    background: #fff;
    color: var(--text);
    border-radius: 10px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: var(--shadow-sm);
  }

  .mobile-nav-button svg {
    width: 18px;
    height: 18px;
  }

  .sidebar-overlay {
    position: fixed;
    inset: 0;
    background: rgba(15, 23, 42, 0.45);
    z-index: 25;
    opacity: 0;
    pointer-events: none;
    transition: opacity .2s;
  }

  body.sidebar-mobile-open .sidebar-overlay,
  .sidebar-overlay.show {
    opacity: 1;
    pointer-events: auto;
  }

  /* ===== 侧边导航 ===== */
  .sidebar {
    width: 280px;
    min-width: 280px;
    background: var(--sidebar-bg);
    padding: 0;
    position: fixed;
    top: 0; left: 0; bottom: 0;
    overflow-y: auto;
    z-index: 10;
    display: flex;
    flex-direction: column;
  }
  .sidebar::-webkit-scrollbar { width: 4px; }
  .sidebar::-webkit-scrollbar-thumb { background: rgba(255,255,255,.15); border-radius: 4px; }
  .sidebar-header {
    padding: 20px 20px 16px;
    border-bottom: 1px solid rgba(255,255,255,.08);
  }
  .sidebar-logo {
    font-size: 18px;
    font-weight: 800;
    color: #fff;
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 4px;
  }
  .sidebar-logo svg { width: 20px; height: 20px; }
  .sidebar-subtitle {
    font-size: 12px;
    color: var(--text-light);
    margin-top: 4px;
  }
  .nav-group { padding: 0 12px; }
  
  .nav-item {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 7px 12px;
    font-size: 13.5px;
    color: var(--sidebar-text);
    text-decoration: none;
    border-radius: 8px;
    transition: all .2s;
    cursor: pointer;
    position: relative;
  }
  .nav-item:hover { background: rgba(255,255,255,.06); color: #fff; }
  .nav-item.active {
    background: var(--sidebar-active-bg);
    color: #a5b4fc;
    font-weight: 600;
  }
  .nav-item.active::before {
    content: '';
    position: absolute;
    left: 0; top: 50%;
    transform: translateY(-50%);
    width: 3px; height: 20px;
    background: var(--primary);
    border-radius: 0 3px 3px 0;
  }
  .nav-sub { padding-left: 12px; }
  .nav-sub .nav-item {
    gap: 8px;
    font-size: 12px;
    line-height: 1.35;
    padding: 4px 12px 4px 28px;
    color: var(--text-light);
  }
  .nav-sub .nav-item:hover, .nav-sub .nav-item.active { color: #a5b4fc; }
  .nav-sub .nav-icon,
  .nav-sub .nav-icon-standalone {
    width: 15px;
    height: 15px;
  }
  .nav-icon {
    width: 18px; height: 18px;
    opacity: .6;
    flex-shrink: 0;
  }
  .nav-item.active .nav-icon { opacity: 1; }
  .nav-icon-standalone {
    margin-right: 10px;
    width: 18px;
    height: 18px;
  }

  /* ===== 主内容 ===== */
  .main {
    flex: 1;
    margin-left: 280px;
    padding: 0;
    min-height: 100vh;
  }

  /* 顶部 Hero */
  .hero {
    background: var(--gradient);
    padding: 36px 40px 28px;
    position: relative;
    overflow: hidden;
  }
  .hero::before {
    content: '';
    position: absolute;
    top: -50%; right: -20%;
    width: 600px; height: 600px;
    background: radial-gradient(circle, rgba(255,255,255,.1) 0%, transparent 70%);
    border-radius: 50%;
  }
  .hero::after {
    content: '';
    position: absolute;
    bottom: -30%; left: 10%;
    width: 400px; height: 400px;
    background: radial-gradient(circle, rgba(255,255,255,.08) 0%, transparent 70%);
    border-radius: 50%;
  }
  .hero-content { position: relative; z-index: 1; }
  .hero h1 {
    font-size: 32px;
    font-weight: 800;
    color: #fff;
    margin-bottom: 4px;
    letter-spacing: -.5px;
  }
  .hero p {
    font-size: 15px;
    color: rgba(255,255,255,.8);
    line-height: 1.6;
  }
  .hero-stats {
    display: flex;
    gap: 32px;
    margin-top: 28px;
  }
  .hero-stat {
    display: flex;
    flex-direction: column;
  }
  .hero-stat-num {
    font-size: 24px;
    font-weight: 800;
    color: #fff;
  }
  .hero-stat-label {
    font-size: 12px;
    color: rgba(255,255,255,.6);
    margin-top: 2px;
  }

  /* 内容区域 */
  .content {
    padding: 0 0 48px;
  }

  /* ===== 章节 ===== */
  .section {
    background: var(--bg);
    border: 1px solid var(--border);
    border-radius: var(--radius);
    padding: 0;
    margin-bottom: 20px;
    box-shadow: var(--shadow-sm);
    overflow: hidden;
    transition: box-shadow .2s;
  }
  .section:hover { box-shadow: var(--shadow); }
  .section-header {
    padding: 24px 28px 20px;
    border-bottom: 1px solid var(--border);
    display: flex;
    align-items: center;
    gap: 14px;
  }
  .section-icon {
    width: 44px; height: 44px;
    border-radius: 12px;
    display: flex; align-items: center; justify-content: center;
    font-size: 18px;
    flex-shrink: 0;
  }
  .section-icon.blue { background: #eff6ff; color: #2563eb; }
  .section-icon.purple { background: #f5f3ff; color: #7c3aed; }
  .section-icon.green { background: #f0fdf4; color: #16a34a; }
  .section-icon.orange { background: #fff7ed; color: #ea580c; }
  .section-icon.pink { background: #fdf2f8; color: #db2777; }
  .section-icon.cyan { background: #ecfeff; color: #0891b2; }
  .section-icon.amber { background: #fffbeb; color: #d97706; }
  .section-icon.red { background: #fef2f2; color: #dc2626; }
  .section-icon.indigo { background: #eef2ff; color: #4f46e5; }
  .section-icon.teal { background: #f0fdfa; color: #0d9488; }
  .section-title {
    font-size: 18px;
    font-weight: 700;
    color: var(--text);
  }
  .section-desc {
    font-size: 13px;
    color: var(--text-secondary);
    margin-top: 2px;
  }
  .section-body {
    padding: 24px 28px 28px;
  }
  .section h3 {
    font-size: 15px;
    font-weight: 700;
    color: var(--text);
    margin: 24px 0 12px;
    display: flex;
    align-items: center;
    gap: 8px;
  }
  .section h3:first-child { margin-top: 0; }
  .h3-dot {
    width: 6px; height: 6px;
    border-radius: 50%;
    background: var(--primary);
    flex-shrink: 0;
  }

  /* 列表 */
  .section ul { padding-left: 0; margin: 8px 0; list-style: none; }
  .section li {
    margin: 0;
    font-size: 14px;
    padding: 6px 0 6px 20px;
    position: relative;
    color: var(--text-secondary);
  }
  .section li::before {
    content: '';
    position: absolute;
    left: 4px; top: 14px;
    width: 6px; height: 6px;
    border-radius: 50%;
    background: var(--border);
  }
  .section li strong { color: var(--text); }
  .section li ul { margin: 4px 0; }
  .section li ul li { font-size: 13px; }

  /* 提示框 */
  .tip {
    border-radius: var(--radius-sm);
    padding: 14px 18px;
    margin: 16px 0;
    font-size: 13px;
    display: flex;
    align-items: center;
    gap: 10px;
  }
  .tip-info {
    background: #eff6ff;
    border: 1px solid #bfdbfe;
    color: #1e40af;
  }
  .tip-info strong { color: #1d4ed8; }
  .tip-warn {
    background: #fffbeb;
    border: 1px solid #fde68a;
    color: #92400e;
  }
  .tip-warn strong { color: #b45309; }
  .tip-icon {
    width: 18px;
    height: 18px;
    flex-shrink: 0;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }
  .tip-icon svg {
    width: 18px;
    height: 18px;
    display: block;
  }

  /* 表格 */
  .table-wrap { overflow-x: auto; margin: 16px 0; border-radius: var(--radius-sm); border: 1px solid var(--border); }
  table {
    width: 100%;
    border-collapse: collapse;
    font-size: 13px;
  }
  th {
    background: var(--bg-alt);
    font-weight: 600;
    text-align: left;
    padding: 12px 16px;
    border-bottom: 2px solid var(--border);
    white-space: nowrap;
    color: var(--text-secondary);
    font-size: 12px;
    text-transform: uppercase;
    letter-spacing: .3px;
  }
  td {
    padding: 12px 16px;
    border-bottom: 1px solid var(--border);
  }
  tr:last-child td { border-bottom: none; }
  tr:hover td { background: var(--primary-light); }

  /* FAQ */
  .faq-item {
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    margin: 10px 0;
    overflow: hidden;
    transition: border-color .2s;
  }
  .faq-item:hover { border-color: #c7d2fe; }
  .faq-q {
    padding: 16px 18px;
    font-weight: 600;
    font-size: 14px;
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: 10px;
    transition: background .15s;
    user-select: none;
  }
  .faq-q:hover { background: var(--bg-alt); }
  .faq-q .arrow {
    transition: transform .25s;
    color: var(--primary);
    font-size: 10px;
    flex-shrink: 0;
    width: 20px; height: 20px;
    background: var(--primary-light);
    border-radius: 50%;
    display: flex; align-items: center; justify-content: center;
  }
  .faq-q.open .arrow { transform: rotate(90deg); background: var(--primary); color: #fff; }
  .faq-a {
    padding: 0 18px 16px 48px;
    font-size: 14px;
    color: var(--text-secondary);
    line-height: 1.7;
    display: none;
  }
  .faq-q.open + .faq-a { display: block; }

  /* 标签 */
  .tag {
    display: inline-flex;
    align-items: center;
    padding: 3px 10px;
    border-radius: 6px;
    font-size: 12px;
    font-weight: 600;
    gap: 4px;
  }
  .tag-blue { background: #dbeafe; color: #1d4ed8; }
  .tag-green { background: #dcfce7; color: #15803d; }
  .tag-yellow { background: #fef9c3; color: #a16207; }
  .tag-gray { background: #f1f5f9; color: #475569; }
  .tag-red { background: #fee2e2; color: #b91c1c; }
  .tag-purple { background: #ede9fe; color: #6d28d9; }

  /* 步骤 */
  .steps { counter-reset: step; list-style: none; padding: 0; margin: 12px 0; }
  .steps li {
    counter-increment: step;
    position: relative;
    padding: 10px 0 10px 48px;
    font-size: 14px;
    color: var(--text-secondary);
  }
  .steps li::before {
    content: counter(step);
    position: absolute;
    left: 0; top: 8px;
    width: 32px; height: 32px;
    background: var(--primary-light);
    color: var(--primary);
    border-radius: 10px;
    font-size: 13px;
    font-weight: 700;
    display: flex; align-items: center; justify-content: center;
    border: 2px solid #c7d2fe;
  }
  .steps li::after {
    content: '';
    position: absolute;
    left: 15px; top: 44px;
    width: 2px;
    height: calc(100% - 36px);
    background: #e2e8f0;
  }
  .steps li:last-child::after { display: none; }
  .steps li strong { color: var(--text); }

  /* 卡片网格 */
  .card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
    gap: 12px;
    margin: 12px 0;
  }
  .card {
    background: var(--bg-alt);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    padding: 16px;
    transition: all .2s;
  }
  .card:hover { border-color: #c7d2fe; background: var(--primary-light); }
  .card-icon { font-size: 24px; margin-bottom: 8px; }
  .card-title { font-size: 13px; font-weight: 700; color: var(--text); margin-bottom: 4px; }
  .card-desc { font-size: 12px; color: var(--text-secondary); line-height: 1.5; }

  /* 功能特性行 */
  .feature-row {
    display: flex;
    gap: 12px;
    margin: 12px 0;
    flex-wrap: wrap;
  }
  .feature-chip {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 10px 16px;
    background: var(--bg-alt);
    border: 1px solid var(--border);
    border-radius: var(--radius-sm);
    font-size: 13px;
    color: var(--text);
    flex: 1;
    min-width: 180px;
  }
  .feature-chip-icon {
    width: 32px; height: 32px;
    border-radius: 8px;
    display: flex; align-items: center; justify-content: center;
    font-size: 16px;
    flex-shrink: 0;
  }

  /* 分隔线 */
  .divider {
    height: 1px;
    background: var(--border);
    margin: 20px 0;
  }

  /* 回到顶部 */
  .back-top {
    position: fixed;
    right: 32px; bottom: 32px;
    width: 44px; height: 44px;
    background: var(--primary);
    color: #fff;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    display: none;
    align-items: center;
    justify-content: center;
    font-size: 18px;
    box-shadow: var(--shadow-lg);
    transition: all .2s;
    z-index: 20;
  }
  .back-top:hover { background: var(--primary-dark); transform: translateY(-2px); }
  .back-top.show { display: flex; }

  /* 公共页脚 */
  .site-footer {
    border-top: 1px solid var(--border);
    background: var(--bg);
    padding: 18px 28px 22px;
  }
  .site-footer-inner {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 6px 16px;
    color: var(--text-secondary);
    font-size: 13px;
    line-height: 1.6;
  }
  .site-footer a {
    color: var(--text-secondary);
    text-decoration: none;
    transition: color .2s;
  }
  .site-footer a:hover {
    color: var(--primary);
  }

  /* 响应式 */
  @media (max-width: 1024px) {
    .content { padding: 0 0 40px; }
    .hero { padding: 28px 28px 22px; }
  }
  @media (max-width: 768px) {
    body.sidebar-mobile-open {
      overflow: hidden;
    }
    .mobile-topbar {
      display: flex;
    }
    .sidebar-overlay {
      display: block;
    }
    .sidebar {
      display: flex;
      width: min(82vw, 320px);
      min-width: min(82vw, 320px);
      transform: translateX(-100%);
      transition: transform .25s ease;
      box-shadow: var(--shadow-lg);
      z-index: 35;
    }
    .sidebar.mobile-open {
      transform: translateX(0);
    }
    .main {
      margin-left: 0;
      padding-top: 56px;
    }
    .hero { padding: 24px 16px 20px; }
    .hero h1 { font-size: 26px; }
    .content { padding: 0 0 32px; }
    .section-header { padding: 20px 20px 16px; }
    .section-body { padding: 20px; }
    .card-grid { grid-template-columns: 1fr; }
    .feature-row { flex-direction: column; }
    .back-top {
      right: 16px;
      bottom: 16px;
    }
  }

  .nav-group-title {
    font-size: 14px;
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: #e2e8f0;
    padding: 8px 12px;
    margin-top: 0;
    display: flex;
    justify-content: space-between;
    align-items: center;
    cursor: pointer;
    user-select: none;
    border-radius: 8px;
    transition: background 0.2s;
  }
  .nav-group-title:hover {
    background: rgba(255, 255, 255, 0.05);
  }
  .nav-group-title .chevron {
    width: 16px;
    height: 16px;
    transition: transform 0.3s;
  }
  .nav-group-content {
    display: none;
    flex-direction: column;
    gap: 2px;
    padding-bottom: 2px;
  }
  .nav-group.expanded .nav-group-content {
    display: flex;
  }
  .nav-group.expanded .nav-group-title .chevron {
    transform: rotate(180deg);
  }
  .nav-group-title.standalone {
    color: #e2e8f0;
    display: flex;
    align-items: center;
  }
  .nav-group-link {
    text-decoration: none;
  }
  .nav-group-title-label {
    display: flex;
    align-items: center;
  }
  .nav-group-title.standalone:hover {
    background: rgba(255,255,255,0.05);
  }
  .nav-group-title.standalone.active {
    color: var(--primary);
    background: var(--sidebar-active-bg);
    border-radius: 8px;
  }