<!DOCTYPE html>
<html>
<head>
  <style>
  body {
    background-color:blue;
  }

  #box {
    width:100px;
    height:100px;
    border:1px solid;
  }
  </style>
</head>
<body>
  <canvas id="box" width="100" height="100">
  </canvas>
</body>
</html>