/* roulang page: index */
:root {
      --primary: #0EA5E9;
      --primary-dark: #0284C7;
      --secondary: #0F172A;
      --accent: #FF6B35;
      --accent-hover: #E55A2B;
      --bg-light: #F8FAFC;
      --bg-gray: #F1F5F9;
      --bg-dark: #0F172A;
      --bg-darker: #0B1120;
      --text-dark: #0F172A;
      --text-gray: #475569;
      --text-light: #94A3B8;
      --border-light: #E2E8F0;
      --border-focus: rgba(14,165,233,0.5);
      --shadow-card: 0 1px 3px rgba(15,23,42,0.06), 0 1px 2px rgba(15,23,42,0.04);
      --shadow-hover: 0 4px 12px rgba(15,23,42,0.08);
      --radius-card: 12px;
      --radius-btn: 8px;
      --radius-input: 6px;
      --font-sans: 'PingFang SC', 'Microsoft YaHei', 'Inter', system-ui, -apple-system, sans-serif;
    }
    * {
      box-sizing: border-box;
    }
    body {
      margin: 0;
      font-family: var(--font-sans);
      background-color: var(--bg-light);
      color: var(--text-dark);
      line-height: 1.75;
      font-size: 16px;
      -webkit-font-smoothing: antialiased;
    }
    img {
      max-width: 100%;
      height: auto;
      display: block;
    }
    a {
      text-decoration: none;
      color: inherit;
    }
    button, input {
      font-family: inherit;
    }
    .container {
      max-width: 1280px;
      margin-left: auto;
      margin-right: auto;
      padding-left: 24px;
      padding-right: 24px;
    }
    /* 导航 */
    .nav-header {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      z-index: 50;
      transition: background 0.3s ease, box-shadow 0.3s ease;
      background: transparent;
      backdrop-filter: blur(0px);
    }
    .nav-header.scrolled {
      background: rgba(248,250,252,0.95);
      backdrop-filter: blur(12px);
      box-shadow: 0 1px 3px rgba(15,23,42,0.08);
      border-bottom: 1px solid #E2E8F0;
    }
    .nav-header.scrolled .nav-logo-text,
    .nav-header.scrolled .nav-link {
      color: var(--secondary);
    }
    .nav-header.scrolled .nav-link:hover {
      color: var(--accent);
    }
    .nav-logo-text {
      font-weight: 700;
      font-size: 1.5rem;
      color: white;
      transition: color 0.3s;
    }
    .nav-header.scrolled .nav-logo-text {
      color: var(--secondary);
    }
    .nav-link {
      color: white;
      font-weight: 500;
      position: relative;
      transition: color 0.2s;
      padding-bottom: 4px;
    }
    .nav-link::after {
      content: '';
      position: absolute;
      bottom: 0;
      left: 50%;
      width: 0;
      height: 2px;
      background: var(--accent);
      transition: width 0.2s ease, left 0.2s ease;
    }
    .nav-link:hover::after {
      width: 100%;
      left: 0;
    }
    .menu-toggle {
      display: none;
      background: none;
      border: none;
      color: white;
      font-size: 1.8rem;
      cursor: pointer;
    }
    .nav-header.scrolled .menu-toggle {
      color: var(--secondary);
    }
    .mobile-menu {
      display: none;
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 100vh;
      background: var(--bg-light);
      flex-direction: column;
      justify-content: center;
      align-items: flex-start;
      padding: 24px;
      z-index: 40;
      gap: 24px;
    }
    .mobile-menu a {
      font-size: 1.5rem;
      font-weight: 600;
      color: var(--secondary);
    }
    /* 按钮 */
    .btn-primary {
      background: var(--accent);
      color: white;
      border: none;
      padding: 12px 28px;
      border-radius: var(--radius-btn);
      font-weight: 600;
      cursor: pointer;
      transition: background 0.2s, transform 0.2s;
      display: inline-block;
      text-align: center;
    }
    .btn-primary:hover {
      background: var(--accent-hover);
      transform: scale(1.03);
    }
    .btn-outline {
      background: transparent;
      border: 2px solid var(--primary);
      color: var(--primary);
      padding: 12px 28px;
      border-radius: var(--radius-btn);
      font-weight: 600;
      cursor: pointer;
      transition: 0.2s;
    }
    .btn-outline:hover {
      background: var(--primary);
      color: white;
    }
    .btn-light {
      background: transparent;
      border: 2px solid white;
      color: white;
      padding: 12px 28px;
      border-radius: var(--radius-btn);
      font-weight: 600;
      cursor: pointer;
      transition: 0.2s;
    }
    .btn-light:hover {
      background: white;
      color: var(--secondary);
    }
    /* 卡片 */
    .card {
      background: white;
      border-radius: var(--radius-card);
      box-shadow: var(--shadow-card);
      border: 1px solid var(--border-light);
      transition: box-shadow 0.2s, border-color 0.2s, transform 0.2s;
    }
    .card:hover {
      box-shadow: var(--shadow-hover);
      border-color: var(--primary);
      transform: translateY(-4px);
    }
    /* 冰雪粒子（仅Hero） */
    .hero-particles {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      overflow: hidden;
      pointer-events: none;
    }
    .particle {
      position: absolute;
      background: white;
      border-radius: 50%;
      opacity: 0.4;
      animation: floatSnow 6s infinite ease-in-out;
    }
    @keyframes floatSnow {
      0% { transform: translateY(0px) scale(0.8); opacity: 0.4; }
      50% { opacity: 0.8; transform: translateY(-30px) scale(1.1); }
      100% { transform: translateY(-10px) scale(0.7); opacity: 0.3; }
    }
    /* FAQ */
    .faq-item {
      border-bottom: 1px solid var(--border-light);
      transition: 0.2s;
    }
    .faq-question {
      cursor: pointer;
      padding: 18px 0;
      font-weight: 600;
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 1.1rem;
    }
    .faq-answer {
      max-height: 0;
      overflow: hidden;
      transition: max-height 0.3s ease, padding 0.3s;
      color: var(--text-gray);
    }
    .faq-item.active .faq-answer {
      max-height: 200px;
      padding-bottom: 18px;
    }
    .faq-item.active {
      border-color: var(--primary);
    }