draw.php first

<?php

print <<<EOF
<!doctype html>
<html>
<style>
  body {
    margin: 30px;
    font-family: Arial, Helvetica, sans-serif;
    background-color: #f0f0f0;
  }

  #mycanvas {
    margin-top: 8px;
    border: 1px #000 solid;
    background-color: #fff;
  }
</style>

<body>
  <!-- import scripts -->
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
  <link rel="stylesheet" href="pickr/dist/themes/classic.min.css" />
  <script src="pickr/dist/pickr.min.js"></script>
  <script src="draw.js"></script>

  <body>
    <input onclick="window.location='index.php'" value="Back" type=button>
    <BR>
    <BR>
    <table>
      <tr>
        <td>
          <div id=picker></div>
        </td>
        <td>
          <input id="pickerButton" type=button value="Choose Color"/>
        </td>
      </tr>
    </table>
    <div>
      <canvas id=mycanvas width=500 height=500></canvas>
    </div>
    <input id=saveButton type=submit value=Save onclick="save($x, $y)">
    <div id=spinner></div>
  </body>
</body>

</html>
EOF;