.container {
      font-family: Arial, sans-serif;
      text-align: center;
      margin-top: 50px;
      background: #f5f5f5;
    }

    .calculator {
      background: #fff;
      padding: 30px;
      border-radius: 10px;
      display: inline-block;
      box-shadow: 0 5px 20px rgba(0,0,0,0.2);
    }

    input {
      padding: 10px;
      width: 200px;
      margin: 10px;
      font-size: 16px;
    }

    select, button {
      padding: 10px;
      font-size: 16px;
      margin: 10px;
    }

    #result {
      margin-top: 20px;
      font-size: 20px;
      font-weight: bold;
    }