body {
      font-family: Arial, sans-serif;
      background-color: #1e1e1e;
      color: white;
      margin: 0;
      padding: 0;
    }
    header {
      background-color: #555;
      padding: 1rem;
      text-align: center;
      color: yellow;
    }
    main { padding: 1rem; }
    button {
      background-color: green;
      color: white;
      font-size: 0.8rem;
      margin: 5px;
      padding: 10px;
      border: none;
      border-radius: 5px;
      cursor: pointer;
    }
    button.reset { background-color: red; }
    .custom-price { margin-bottom: 1rem; }
    #invoice {
      display: none;
      font-family: monospace;
      color: black;
      background: white;
      padding: 10px;
      width: 240px;
    }
    #invoice h2 { text-align: center; font-size: 1.2em; }
    #invoice hr { border: none; border-top: 1px dashed black; }
    @media print {
      body * { visibility: hidden; }
      #invoice, #invoice * { visibility: visible; }
      #invoice { position: absolute; left: 0; top: 0; }
    }