date-picker.html

<html>
  <head>
    <link rel="stylesheet" href="https://trello.com/power-ups/power-up.css">
    <link rel="stylesheet" href="./date-picker.css">
    <link rel="stylesheet" href="./style/spinner.css">
    <script src="https://trello.com/power-ups/power-up.min.js"></script>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.3/jquery.min.js"></script>
    <script src="https://api.trello.com/1/client.js?key=029a2bec58250bca0e3f1a29451f13ce"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.15.1/moment.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/moment-timezone/0.5.6/moment-timezone-with-data.min.js"></script>

  </head>
  <body>
    <div id="content" style="display: flex; flex-direction: column;">
    </div>
    <script src="./date-picker.js"></script>
  </body>
</html>