body {
      font-family: 'Segoe UI', sans-serif;
      background: #f4f4f4;
      margin: 0;
      padding: 0;
    }
    .navbar {
      background-color: #333;
      overflow: hidden;
    }
    .navbar a {
      float: left;
      display: block;
      color: white;
      text-align: center;
      padding: 14px 16px;
      text-decoration: none;
    }
    .dropdown {
      float: left;
      overflow: hidden;
    }
    .dropdown .dropbtn {
      font-size: 16px;
      border: none;
      outline: none;
      color: white;
      padding: 14px 16px;
      background-color: inherit;
      font-family: inherit;
      margin: 0;
    }
    .navbar a:hover,
    .dropdown:hover .dropbtn {
      background-color: #555;
    }
    .dropdown-content {
      display: none;
      position: absolute;
      background-color: #f9f9f9;
      min-width: 160px;
      box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
      z-index: 1;
    }
    .dropdown-content a {
      float: none;
      color: black;
      padding: 12px 16px;
      text-decoration: none;
      display: block;
      text-align: left;
    }
    .dropdown-content a:hover {
      background-color: #ddd;
    }
    .dropdown:hover .dropdown-content {
      display: block;
    }
    .container {
      max-width: 640px;
      margin: 80px auto 20px;
      background: #fff;
      padding: 25px;
      border-radius: 12px;
      box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
    }
    h2 {
      text-align: center;
      margin-bottom: 20px;
    }
    select,
    textarea {
      width: 100%;
      padding: 12px;
      margin-top: 10px;
      font-size: 16px;
      border-radius: 8px;
      border: 1px solid #ccc;
      box-sizing: border-box;
    }
    .output {
      margin-top: 20px;
      padding: 15px;
      background: #fff;
      border: 1px solid #ddd;
      border-radius: 6px;
      font-size: 18px;
      color: #222;
      min-height: 60px;
      position: relative;
    }
    label {
      margin-top: 10px;
      display: block;
      font-weight: bold;
    }
    .footer {
      text-align: center;
      margin-top: 30px;
      font-size: 14px;
      color: #999;
    }
    .copy-container {
      display: flex;
      align-items: center;
      gap: 10px;
      margin-top: 10px;
    }
    .copy-btn {
      background: #007bff;
      color: white;
      border: none;
      padding: 8px 12px;
      border-radius: 6px;
      cursor: pointer;
      font-size: 14px;
    }
    .swap-btn {
      margin-top: 6px;
      background: #fff;
      border: 1px solid #ccc;
      padding: 6px 10px;
      border-radius: 6px;
      cursor: pointer;
      font-size: 18px;
    }