:root {
      --primary-color: #2c3e50;
      --accent-color: #3498db;
      --bg-color: #ecf0f1;
      --card-bg: #ffffff;
      --font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
      --border-radius: 8px;
      --shadow: 0 2px 8px rgba(0,0,0,0.1);
    }
    * {
      box-sizing: border-box;
    }
    body {
      margin: 0;
      font-family: var(--font-family);
      background-color: var(--bg-color);
      color: var(--primary-color);
      line-height: 1.6;
    }
    header {
      background: linear-gradient(135deg, var(--primary-color) 0%, #34495e 100%);
      color: white;
      padding: 3rem 1rem;
      text-align: center;
      box-shadow: var(--shadow);
    }
    header h1 {
      margin: 0;
      font-size: 2.5rem;
      font-weight: 600;
    }
    header p {
      margin: 0.5rem 0 0;
      font-size: 1.3rem;
      opacity: 0.95;
    }
    nav {
      background: white;
      padding: 1rem;
      box-shadow: var(--shadow);
    }
    nav .container {
      max-width: 1100px;
      margin: 0 auto;
    }
    nav a {
      color: var(--accent-color);
      text-decoration: none;
      font-weight: 500;
    }
    nav a:hover {
      text-decoration: underline;
    }
    main {
      padding: 2rem 1rem;
      max-width: 1100px;
      margin: 0 auto;
    }
    .course-content {
      background: var(--card-bg);
      border-radius: var(--border-radius);
      box-shadow: var(--shadow);
      padding: 2rem;
    }
    .course-meta {
      display: flex;
      flex-wrap: wrap;
      gap: 1rem;
      margin-bottom: 1.5rem;
      padding: 1rem;
      background: #f8f9fa;
      border-radius: 6px;
      border-left: 4px solid var(--accent-color);
    }
    .course-meta > p {
      margin: 0;
      flex: 1 1 200px;
    }
    .course-overview {
      background: #e8f4f8;
      padding: 1rem 1.5rem;
      border-radius: 6px;
      margin: 1rem 0;
      border-left: 4px solid var(--accent-color);
    }
    .course-overview p {
      margin: 0;
    }
    h2 {
      color: var(--primary-color);
      font-size: 1.8rem;
      border-bottom: 3px solid var(--accent-color);
      padding-bottom: 0.5rem;
      margin-bottom: 1.5rem;
    }
    h3 {
      color: var(--accent-color);
      font-size: 1.4rem;
      margin-top: 1.5rem;
      margin-bottom: 0.75rem;
    }
    h4 {
      color: var(--primary-color);
      font-size: 1.1rem;
      margin-top: 1.25rem;
      margin-bottom: 0.5rem;
      font-weight: 600;
    }
    ul {
      margin: 0.5rem 0 1rem 0;
      padding-left: 1.5rem;
    }
    ul li {
      margin-bottom: 0.5rem;
    }
    details {
      margin: 1rem 0;
      padding: 1rem;
      background: #f8f9fa;
      border-radius: 6px;
      cursor: pointer;
    }
    details summary {
      font-weight: 600;
      color: var(--accent-color);
      cursor: pointer;
      user-select: none;
      list-style: none;
    }
    details summary::-webkit-details-marker {
      display: none;
    }
    details summary::before {
      content: '▶ ';
      display: inline-block;
      transition: transform 0.2s;
    }
    details[open] summary::before {
      transform: rotate(90deg);
    }
    details[open] {
      background: white;
      border: 1px solid #dee2e6;
    }
    footer {
      text-align: center;
      padding: 2rem 1rem;
      font-size: 0.9rem;
      color: #777;
      background: white;
      margin-top: 2rem;
      box-shadow: 0 -2px 8px rgba(0,0,0,0.05);
    }
    footer a {
      color: var(--accent-color);
      text-decoration: none;
    }
    footer a:hover {
      text-decoration: underline;
    }
    @media (max-width: 768px) {
      header h1 {
        font-size: 1.8rem;
      }
      .course-content {
        padding: 1.5rem;
      }
      .course-meta {
        flex-direction: column;
      }
    }