/* 全局样式重置与基础设置 */
    * {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    }
    
    :root {
      --primary: #165DFF;
      --primary-light: #4080FF;
      --secondary: #FF7D00;
      --dark: #1D2129;
      --gray: #4E5969;
      --light-gray: #F2F3F5;
      --white: #FFFFFF;
      --shadow: 0 4px 20px rgba(0, 0, 0, 0.08);
      --transition: all 0.3s ease;
    }
    
    body {
      background-color: #FAFAFA;
      color: var(--dark);
      line-height: 1.6;
    }
    
    .container {
      max-width: 1200px;
      margin: 0 auto;
      padding: 0 20px;
    }
    
    /* 导航栏样式 */
    .navbar {
      background-color: var(--white);
      box-shadow: var(--shadow);
      position: sticky;
      top: 0;
      z-index: 100;
    }
    
    .nav-container {
      display: flex;
      justify-content: space-between;
      align-items: center;
      padding: 15px 20px;
    }
    
    .logo {
      display: flex;
      align-items: center;
      gap: 10px;
      color: var(--primary);
      font-size: 24px;
      font-weight: 700;
      text-decoration: none;
    }
    
    .nav-menu {
      display: flex;
      list-style: none;
      gap: 30px;
    }
    
    .nav-link {
      color: var(--dark);
      text-decoration: none;
      font-weight: 500;
      transition: var(--transition);
    }
    
    .nav-link:hover {
      color: var(--primary);
    }
    
    .nav-actions {
      display: flex;
      gap: 15px;
    }
    
    .btn {
      padding: 8px 16px;
      border-radius: 6px;
      border: none;
      cursor: pointer;
      font-weight: 500;
      transition: var(--transition);
      text-decoration: none;
      display: inline-block;
    }
    
    .btn-outline {
      background: transparent;
      border: 1px solid var(--primary);
      color: var(--primary);
    }
    
    .btn-primary {
      background-color: var(--primary);
      color: var(--white);
    }
    
    .btn-primary:hover {
      background-color: var(--primary-light);
    }
    
    /* 页面区域样式 */
    .section {
      padding: 60px 0;
    }
    
    .section-title {
      text-align: center;
      margin-bottom: 40px;
    }
    
    .section-title h2 {
      font-size: 32px;
      margin-bottom: 10px;
      color: var(--dark);
    }
    
    .section-title p {
      color: var(--gray);
      max-width: 600px;
      margin: 0 auto;
    }
    
    /* 课程列表样式 */
    .courses-grid {
      display: grid;
      grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
      gap: 30px;
    }
    
    .course-card {
      background: var(--white);
      border-radius: 12px;
      overflow: hidden;
      box-shadow: var(--shadow);
      transition: var(--transition);
      cursor: pointer;
    }
    
    .course-card:hover {
      transform: translateY(-5px);
      box-shadow: 0 10px 25px rgba(22, 93, 255, 0.15);
    }
    
    .course-img {
      width: 100%;
      height: 160px;
      object-fit: cover;
    }
    
    .course-info {
      padding: 20px;
    }
    
    .course-category {
      display: inline-block;
      background-color: rgba(22, 93, 255, 0.1);
      color: var(--primary);
      padding: 3px 8px;
      border-radius: 4px;
      font-size: 12px;
      margin-bottom: 10px;
    }
    
    .course-title {
      font-size: 18px;
      font-weight: 600;
      margin-bottom: 10px;
      display: -webkit-box;
      -webkit-line-clamp: 2;
      -webkit-box-orient: vertical;
      overflow: hidden;
    }
    
    .course-meta {
      display: flex;
      justify-content: space-between;
      color: var(--gray);
      font-size: 14px;
      margin-bottom: 15px;
    }
    
    .course-price {
      display: flex;
      align-items: center;
      gap: 10px;
    }
    
    .price-new {
      color: var(--secondary);
      font-size: 20px;
      font-weight: 700;
    }
    
    .price-old {
      color: var(--gray);
      text-decoration: line-through;
      font-size: 14px;
    }
    
    /* 课程详情页样式 */
    .course-header {
      background-color: var(--white);
      padding: 40px 0;
      box-shadow: var(--shadow);
    }
    
    .course-header-content {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 40px;
      align-items: center;
    }
    
    .course-detail-img {
      width: 100%;
      border-radius: 12px;
    }
    
    .course-detail-info h1 {
      font-size: 28px;
      margin-bottom: 15px;
    }
    
    .course-detail-desc {
      color: var(--gray);
      margin-bottom: 20px;
    }
    
    .course-features {
      display: flex;
      flex-wrap: wrap;
      gap: 20px;
      margin-bottom: 25px;
    }
    
    .feature {
      display: flex;
      align-items: center;
      gap: 8px;
    }
    
    .course-detail-price {
      margin-bottom: 25px;
    }
    
    .course-content {
      padding: 60px 0;
    }
    
    .content-tabs {
      display: flex;
      gap: 30px;
      margin-bottom: 30px;
      border-bottom: 1px solid var(--light-gray);
      padding-bottom: 15px;
    }
    
    .tab {
      font-weight: 600;
      cursor: pointer;
      position: relative;
    }
    
    .tab.active::after {
      content: '';
      position: absolute;
      bottom: -15px;
      left: 0;
      width: 100%;
      height: 3px;
      background-color: var(--primary);
    }
    
    .chapter-list {
      background: var(--white);
      border-radius: 8px;
      overflow: hidden;
    }
    
    .chapter-item {
      border-bottom: 1px solid var(--light-gray);
    }
    
    .chapter-header {
      padding: 15px 20px;
      background-color: var(--light-gray);
      font-weight: 600;
      display: flex;
      justify-content: space-between;
      align-items: center;
      cursor: pointer;
    }
    
    .lesson-list {
      padding: 10px 20px;
    }
    
    .lesson-item {
      padding: 12px 0;
      display: flex;
      justify-content: space-between;
      align-items: center;
      border-bottom: 1px solid #f0f0f0;
    }
    
    .lesson-item:last-child {
      border-bottom: none;
    }
    
    .lesson-title {
      display: flex;
      align-items: center;
      gap: 10px;
    }
    
    /* 视频播放页样式 */
    .video-player-section {
      padding: 30px 0;
    }
    
    .video-container {
      background-color: #000;
      border-radius: 12px;
      overflow: hidden;
      margin-bottom: 30px;
      position: relative;
    }
    
    .video-player {
      width: 100%;
      display: block;
      aspect-ratio: 16/9;
    }
    
    .video-info {
      background: var(--white);
      padding: 20px;
      border-radius: 8px;
      margin-bottom: 30px;
    }
    
    .video-title {
      font-size: 22px;
      margin-bottom: 10px;
    }
    
    .video-navigation {
      display: flex;
      justify-content: space-between;
      margin-top: 20px;
    }
    
    /* 页脚样式 */
    .footer {
      background-color: var(--dark);
      color: var(--white);
      padding: 60px 0 20px;
    }
    
    .footer-content {
      display: grid;
      grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
      gap: 40px;
      margin-bottom: 40px;
    }
    
    .footer-column h3 {
      font-size: 18px;
      margin-bottom: 20px;
      color: var(--white);
    }
    
    .footer-links {
      list-style: none;
    }
    
    .footer-link {
      color: #C9CDD4;
      text-decoration: none;
      display: block;
      margin-bottom: 10px;
      transition: var(--transition);
    }
    
    .footer-link:hover {
      color: var(--primary-light);
    }
    
    .social-links {
      display: flex;
      gap: 15px;
      margin-top: 20px;
    }
    
    .social-link {
      color: var(--white);
      width: 36px;
      height: 36px;
      border-radius: 50%;
      background-color: rgba(255, 255, 255, 0.1);
      display: flex;
      align-items: center;
      justify-content: center;
      transition: var(--transition);
    }
    
    .social-link:hover {
      background-color: var(--primary);
    }
    
    .copyright {
      text-align: center;
      padding-top: 20px;
      border-top: 1px solid rgba(255, 255, 255, 0.1);
      color: #86909C;
    }
    
    /* 响应式适配 */
    @media (max-width: 768px) {
      .nav-menu {
        display: none;
      }
      
      .course-header-content {
        grid-template-columns: 1fr;
      }
      
      .section-title h2 {
        font-size: 26px;
      }
    }
    
    /* 页面切换控制 */
    .page {
      display: none;
    }
    
    .page.active {
      display: block;
    }