body {
    font-family: Helvetica, Arial, sans-serif;
    background-color: #f0f0f0;
    margin: 0;
    padding: 20px;
  }
  
  #container {
    max-width: 400px;
    margin: 0 auto;
    background: #ffffff;
    border-radius: 8px;
    padding: 20px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
  }
  
  h1 {
    text-align: center;
    margin-bottom: 20px;
  }
  
  label {
    font-size: 16px;
    display: block;
    margin-top: 10px;
  }
  
  input, button {
    width: 100%;
    padding: 10px;
    margin-top: 5px;
    border: 1px solid #ccc;
    border-radius: 4px;
    box-sizing: border-box;
    font-size: 16px;
  }
  
  button {
    background-color: #007BFF;
    color: #fff;
    border: none;
    cursor: pointer;
    margin-top: 15px;
  }
  
  button:hover {
    background-color: #0056b3;
  }
  
  .hidden {
    display: none;
  }
  
  .result {
    margin-top: 20px;
    font-size: 18px;
    padding: 10px;
    background: #e9ecef;
    border-radius: 4px;
  }
  
  .back-btn {
    background-color: #6c757d;
  }