body {
      font-family: Arial, sans-serif;
      margin: 0;
      padding: 0;
      background: #f4f4f4;
      transition: background 0.5s ease-in-out;
    }
    .container {
      max-width: 900px;
      margin: auto;
      padding: 20px;
      background: white;
      box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
      border-radius: 8px;
    }
    header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      padding: 20px;
      background: #0073e6;
      color: white;
      border-radius: 8px 8px 0 0;
    }
    .responsive-heading a {
      margin: 0 10px;
      color: white;
      text-decoration: none;
      transition: color 0.3s;
    }
    .responsive-heading a:hover {
      color: #ffdd57;
    }
    section {
      display: none;
      opacity: 0;
      transition: opacity 0.5s;
    }
    .active {
      display: block;
      opacity: 1;
    }
    .fade-in {
      animation: fadeIn 1s ease-in-out;
    }
    @keyframes fadeIn {
      from { opacity: 0; transform: translateY(-10px); }
      to { opacity: 1; transform: translateY(0); }
    }