body {
    font-family: sans-serif;
    background: #f2f2f2;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
  }
  
  .container {
    background: white;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    text-align: center;
    width: 320px;
  }
  
  input, button {
    padding: 10px;
    margin: 10px 5px;
    font-size: 1rem;
    width: 80%;
  }
  
  button {
    cursor: pointer;
  }
  
  #change-due {
    margin-top: 20px;
    font-weight: bold;
  }