/* roulang page: index */
/* ----- 设计变量 & 基础重置 ----- */
    :root {
      --primary: #E8452D;
      --primary-hover: #C0392B;
      --primary-soft: rgba(232, 69, 45, 0.08);
      --dark-charcoal: #1E1E1E;
      --track-black: #0B0B0B;
      --gold: #F5A623;
      --white: #FFFFFF;
      --bg-light: #F8F9FA;
      --gray-text: #4A4A4A;
      --gray-mid: #7A7A7A;
      --gray-light: #9A9A9A;
      --border-light: #E0E0E0;
      --shadow-card: 0 2px 12px rgba(0,0,0,0.06);
      --shadow-hover: 0 8px 24px rgba(0,0,0,0.12);
      --radius-card: 12px;
      --radius-btn: 8px;
      --transition: 0.25s ease-in-out;
      --font-sans: 'PingFang SC', 'Microsoft YaHei', 'Helvetica Neue', system-ui, -apple-system, sans-serif;
      --font-number: 'Segoe UI', 'Roboto', 'Helvetica Neue', sans-serif;
    }
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
    }
    html {
      scroll-behavior: smooth;
    }
    body {
      font-family: var(--font-sans);
      background-color: var(--white);
      color: var(--gray-text);
      line-height: 1.6;
      font-size: 16px;
      -webkit-font-smoothing: antialiased;
    }
    img {
      max-width: 100%;
      height: auto;
      display: block;
    }
    a {
      text-decoration: none;
      color: inherit;
      transition: color var(--transition);
    }
    button, .btn {
      cursor: pointer;
      font-family: inherit;
      border: none;
      background: none;
    }
    .container {
      width: 100%;
      max-width: 1200px;
      margin: 0 auto;
      padding: 0 20px;
    }
    /* 排版辅助 */
    h2 {
      font-size: 2.5rem;
      font-weight: 700;
      line-height: 1.3;
      color: var(--dark-charcoal);
      margin-bottom: 1rem;
      letter-spacing: -0.02em;
    }
    h3 {
      font-size: 1.5rem;
      font-weight: 600;
      color: var(--dark-charcoal);
    }
    .section {
      padding: 100px 0;
    }
    @media (max-width: 768px) {
      h2 {
        font-size: 2rem;
      }
      .section {
        padding: 60px 0;
      }
    }
    /* ----- 导航 (固定白底平台) ----- */
    .nav {
      position: fixed;
      top: 0;
      left: 0;
      width: 100%;
      height: 72px;
      background: rgba(255,255,255,0.96);
      backdrop-filter: blur(8px);
      box-shadow: 0 2px 8px rgba(0,0,0,0.04);
      z-index: 100;
      display: flex;
      align-items: center;
      transition: box-shadow 0.3s;
    }
    .nav.scrolled {
      box-shadow: 0 4px 16px rgba(0,0,0,0.08);
    }
    .nav-container {
      display: flex;
      justify-content: space-between;
      align-items: center;
      width: 100%;
    }
    .logo {
      font-size: 1.8rem;
      font-weight: 700;
      color: var(--primary);
      letter-spacing: 0.5px;
      display: flex;
      align-items: center;
      gap: 8px;
    }
    .logo span {
      background: var(--primary);
      color: white;
      width: 32px;
      height: 32px;
      border-radius: 8px;
      display: inline-flex;
      align-items: center;
      justify-content: center;
      font-size: 1.2rem;
      margin-right: 4px;
    }
    .nav-menu {
      display: flex;
      gap: 2.2rem;
      list-style: none;
    }
    .nav-menu a {
      font-size: 0.95rem;
      font-weight: 500;
      color: var(--dark-charcoal);
      position: relative;
      padding: 6px 0;
    }
    .nav-menu a::after {
      content: '';
      position: absolute;
      bottom: 0;
      left: 0;
      width: 0;
      height: 2px;
      background: var(--primary);
      transition: width 0.2s ease;
    }
    .nav-menu a:hover {
      color: var(--primary);
    }
    .nav-menu a:hover::after {
      width: 100%;
    }
    .hamburger {
      display: none;
      flex-direction: column;
      gap: 5px;
      background: transparent;
      border: none;
      cursor: pointer;
    }
    .hamburger span {
      width: 26px;
      height: 2.5px;
      background: var(--dark-charcoal);
      border-radius: 2px;
      transition: 0.2s;
    }
    @media (max-width: 768px) {
      .nav-menu {
        position: fixed;
        top: 0;
        right: -100%;
        width: 70%;
        max-width: 300px;
        height: 100vh;
        background: var(--track-black);
        flex-direction: column;
        padding: 100px 30px 30px;
        gap: 2rem;
        transition: right 0.3s ease;
        box-shadow: -5px 0 20px rgba(0,0,0,0.2);
      }
      .nav-menu.active {
        right: 0;
      }
      .nav-menu a {
        color: white;
        font-size: 1.2rem;
      }
      .hamburger {
        display: flex;
        z-index: 110;
      }
    }
    /* ----- 首屏 Hero ----- */
    .hero {
      min-height: 100vh;
      display: flex;
      align-items: center;
      background: linear-gradient(135deg, #0B0B0B 0%, #1E1E1E 100%);
      position: relative;
      overflow: hidden;
      padding-top: 72px;
    }
    .hero::before {
      content: '';
      position: absolute;
      width: 60%;
      height: 100%;
      right: -5%;
      top: 0;
      background: radial-gradient(circle at 30% 40%, rgba(232,69,45,0.15) 0%, transparent 60%);
      pointer-events: none;
    }
    .hero-grid {
      display: flex;
      align-items: center;
      gap: 3rem;
      position: relative;
      z-index: 2;
    }
    .hero-text {
      flex: 1 1 50%;
    }
    .hero-text h1 {
      font-size: 3.5rem;
      font-weight: 800;
      line-height: 1.15;
      color: white;
      margin-bottom: 1.5rem;
      letter-spacing: -0.02em;
    }
    .hero-text h1 .highlight {
      color: var(--primary);
    }
    .hero-sub {
      font-size: 1.2rem;
      color: #CCCCCC;
      margin-bottom: 2.2rem;
      max-width: 450px;
    }
    .hero-buttons {
      display: flex;
      gap: 1.2rem;
      flex-wrap: wrap;
    }
    .btn-primary {
      background: var(--primary);
      color: white;
      padding: 14px 32px;
      border-radius: var(--radius-btn);
      font-weight: 600;
      font-size: 1rem;
      transition: all 0.2s;
      box-shadow: 0 4px 12px rgba(232,69,45,0.3);
      border: none;
    }
    .btn-primary:hover {
      background: var(--primary-hover);
      transform: scale(1.03);
      box-shadow: 0 8px 18px rgba(192,57,43,0.4);
    }
    .btn-outline {
      background: transparent;
      border: 2px solid rgba(255,255,255,0.6);
      color: white;
      padding: 14px 32px;
      border-radius: var(--radius-btn);
      font-weight: 600;
      transition: 0.2s;
    }
    .btn-outline:hover {
      background: white;
      color: var(--dark-charcoal);
    }
    .hero-image {
      flex: 1 1 50%;
      position: relative;
    }
    .hero-image img {
      border-radius: 20px;
      box-shadow: 0 20px 40px rgba(0,0,0,0.5);
      transform: perspective(800px) rotateY(-3deg);
      transition: 0.3s;
      max-height: 500px;
      object-fit: cover;
      width: 100%;
    }
    @media (max-width: 768px) {
      .hero-grid {
        flex-direction: column;
        text-align: center;
      }
      .hero-text h1 {
        font-size: 2.5rem;
      }
      .hero-sub {
        margin-left: auto;
        margin-right: auto;
      }
      .hero-buttons {
        justify-content: center;
      }
      .hero-image img {
        transform: none;
        max-height: 320px;
      }
    }
    /* ----- 优势卡片（数字序号） ----- */
    .advantages-grid {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 28px;
      margin-top: 2.5rem;
    }
    .adv-card {
      background: white;
      border: 1px solid var(--border-light);
      border-radius: var(--radius-card);
      padding: 30px 24px;
      display: flex;
      align-items: flex-start;
      gap: 20px;
      transition: all 0.25s;
      box-shadow: var(--shadow-card);
    }
    .adv-card:hover {
      box-shadow: var(--shadow-hover);
      transform: translateY(-4px);
    }
    .adv-number {
      font-family: var(--font-number);
      font-size: 3rem;
      font-weight: 700;
      color: rgba(232,69,45,0.2);
      line-height: 1;
      transition: 0.2s;
    }
    .adv-card:hover .adv-number {
      color: var(--primary);
      opacity: 1;
    }
    .adv-content h3 {
      margin-bottom: 0.5rem;
    }
    @media (max-width: 768px) {
      .advantages-grid {
        grid-template-columns: 1fr;
      }
    }
    /* ----- 服务体系 交错布局 ----- */
    .service-row {
      display: flex;
      align-items: center;
      gap: 3rem;
      margin-bottom: 80px;
    }
    .service-row.reverse {
      flex-direction: row-reverse;
    }
    .service-img {
      flex: 1;
    }
    .service-img img {
      border-radius: 16px;
      box-shadow: 0 8px 20px rgba(0,0,0,0.1);
      aspect-ratio: 1/1;
      object-fit: cover;
    }
    .service-text {
      flex: 1;
    }
    @media (max-width: 768px) {
      .service-row, .service-row.reverse {
        flex-direction: column;
      }
    }
    /* ----- 数据背书 ----- */
    .data-bg {
      background: #F0F2F5;
      border-radius: 28px;
      padding: 50px 30px;
    }
    .data-grid {
      display: grid;
      grid-template-columns: repeat(4, 1fr);
      gap: 30px;
      text-align: center;
    }
    .data-item .number {
      font-family: var(--font-number);
      font-size: 2.8rem;
      font-weight: 700;
      color: var(--primary);
    }
    @media (max-width: 768px) {
      .data-grid {
        grid-template-columns: repeat(2, 1fr);
      }
    }
    /* ----- 案例卡片 (封面遮罩) ----- */
    .cases-grid {
      display: grid;
      grid-template-columns: repeat(3, 1fr);
      gap: 24px;
    }
    .case-card {
      height: 320px;
      border-radius: var(--radius-card);
      background-size: cover;
      background-position: center;
      position: relative;
      overflow: hidden;
      display: flex;
      align-items: flex-end;
      transition: 0.3s;
    }
    .case-card::after {
      content: '';
      position: absolute;
      bottom: 0;
      width: 100%;
      height: 60%;
      background: linear-gradient(to top, rgba(0,0,0,0.8), transparent);
    }
    .case-info {
      position: relative;
      z-index: 2;
      color: white;
      padding: 24px;
      transform: translateY(0);
      transition: 0.25s;
    }
    .case-card:hover .case-info {
      transform: translateY(-8px);
    }
    @media (max-width: 768px) {
      .cases-grid {
        grid-template-columns: 1fr;
      }
    }
    /* ----- FAQ 手风琴 ----- */
    .faq-item {
      border-bottom: 1px solid var(--border-light);
      padding: 18px 0;
      cursor: pointer;
    }
    .faq-question {
      font-weight: 600;
      font-size: 1.1rem;
      display: flex;
      justify-content: space-between;
      align-items: center;
      color: var(--dark-charcoal);
      position: relative;
    }
    .faq-answer {
      max-height: 0;
      overflow: hidden;
      transition: max-height 0.3s ease;
      color: var(--gray-mid);
    }
    .faq-item.active .faq-answer {
      max-height: 200px;
      margin-top: 12px;
    }
    /* CTA 与页脚 */
    .cta-band {
      background: var(--track-black);
      text-align: center;
      padding: 80px 20px;
      color: white;
    }
    .footer {
      background: var(--track-black);
      color: var(--gray-light);
      padding: 60px 0 20px;
    }
    .footer-grid {
      display: grid;
      grid-template-columns: 2fr 1fr 1fr 1fr;
      gap: 30px;
    }
    @media (max-width: 768px) {
      .footer-grid {
        grid-template-columns: 1fr 1fr;
      }
    }