 card number <code>4111 1111 1111 1111</code>.
    </p>

    <button id="checkout-button">Checkout</button>
  </div>
  
  <div id="success">
    <p>
      Payment Request success. Demo complete. No payment has been taken.
    </p>
  </div>

  <div id="legacy">
    <p>
      The Payment Request API is unsupported or was cancelled or failed, 
      so here we can proceed with our legacy web form (not implemented for this demo).
    </p>
  </div>

  <script type="text/javascript">
    
    var checkoutButton =