html, body {
    margin: 0;
    padding: 0;
  }
  canvas {
    padding: 0;
    margin: auto;
    display: block;
    width: 800px;
    height: 600px;
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;
    border-top: 1px solid black;
    border-left: 1px solid black;
  }