body {
      font-family: 'Sarabun', sans-serif;
      margin: 0;
      background-color: #f8f9fa;
      color: #333;
    }

    .container {
      display: flex;
      max-width: 1400px;
      margin: 2rem auto;
      padding: 0 1.5rem;
      gap: 2rem;
    }

    .sidebar {
      width: 25%;
      min-width: 240px;
      flex-shrink: 0;
    }

    .sidebar h4 {
      font-size: 1.1rem;
      padding-left: 1rem;
      border-left: 4px solid #00897b;
      margin-top: 0;
    }

    .sidebar ul {
      list-style: none;
      padding: 0;
      margin: 0;
    }

    .sidebar ul li a {
      display: block;
      padding: 12px 15px;
      text-decoration: none;
      color: #555;
      border-radius: 6px;
      margin-bottom: 5px;
      transition: all 0.2s ease-in-out;
    }

    .sidebar ul li a:hover,
    .sidebar ul li a.active {
      background-color: #e8f5e9;
      color: #2e7d32;
      font-weight: 500;
    }

    .content {
      width: 75%;
    }

    .main-header h2 {
      font-size: 1.5rem;
      margin-bottom: 1.5rem;
    }

    .course-list {
      display: grid;
      grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
      gap: 1.5rem;
    }

    .course-card {
      background-color: white;
      border: 1px solid #e0e0e0;
      border-radius: 8px;
      padding: 1.5rem;
      display: flex;
      flex-direction: column;
      box-shadow: 0 1px 3px rgba(0,0,0,0.05);
      height: 100%;
    }

    .course-icon {
      background-color: #26c6da;
      color: white;
      border-radius: 50%;
      width: 56px;
      height: 56px;
      display: flex;
      align-items: center;
      justify-content: center;
      margin-bottom: 1rem;
    }

    .course-icon svg {
      width: 28px;
      height: 28px;
    }

    .course-details h3 {
      margin: 0 0 4px 0;
      font-size: 1.3rem;
    }

    .course-details p {
      margin: 0;
      color: #616161;
      font-size: 0.95rem;
    }

    .course-info {
      font-size: 0.9rem;
      color: #757575;
      margin-top: 4px;
    }

    .course-action {
      margin-top: 1rem;
      display: flex;
      justify-content: flex-end;
    }

    .register-btn {
      background-color: #4caf50;
      color: white;
      padding: 10px 28px;
      text-decoration: none;
      border-radius: 5px;
      font-weight: 500;
      white-space: nowrap;
      transition: background-color 0.3s ease;
    }

    .register-btn:hover {
      background-color: #43a047;
    }

    @media (max-width: 768px) {
      .container {
        flex-direction: column;
      }
      .sidebar, .content {
        width: 100%;
      }
    }