body {

      --color-text: #000;
      --color-background: #f7f7f7;
      --color-card: #fff;
      --color-datetime: #666;
      --color-error: #b00;

      @media (prefers-color-scheme: dark) {
        --color-text: #fff;
        --color-background: #111;
        --color-card: #000;
        --color-datetime: #aaa;
        --color-error: #b66;

        #qrcode > img, #qrcode > canvas {
          --darkreader-background-ffffff: #fff !important;
          background-color: #fff !important;
        }
      }

      color: var(--color-text);

      font-family: system-ui, sans-serif;
      display: flex;
      align-items: center;
      justify-content: center;
      height: 100vh;
      background: var(--color-background);
      margin: 0;
    }
    .card {
      background: var(--color-card);
      padding: 2rem;
      border-radius: 1rem;
      box-shadow: 0 4px 20px rgba(0,0,0,0.1);
      text-align: center;
      max-width: 400px;
    }
    h1 {
      margin-bottom: 0.5rem;
    }
    .date, .time {
      color: var(--color-datetime);
      font-size: 0.9rem;
    }
    #qrcode {
      margin: 2rem auto 0;
      display: flex;
      justify-content: center;
    }
    #qrcode > img, #qrcode > canvas {
      padding: 0.5em;
      background-color: #fff !important;
    }
    .error {
      text-align: center;
      font-size: 1.2rem;
      color: var(--color-error);
    }