Untitled

<!DOCTYPE html>
<html>
<head>
  <meta name="viewport" content="user-scalable=no,initial-scale=1.0,maximum-scale=1.0" />

  <style>
  body { padding:10px; margin:0px; background-color: #ccc; }
  #main { margin: 10px auto 0px auto; }
  </style>

  <script src="draw.js"></script>
</head>
<body>
<button id="clear">clear</button><br>
<canvas id="main" width="300" height="300"></canvas>
</body>
</html>