html {
  display: table;
  width: 100%;
  height: 100%;
}

body {
  display: table-cell;
  vertical-align: middle;
  text-align: center;
  background: #222;
}

canvas {
  display: block;
  margin: auto;
  width: 640px;
  height: 360px;
  background: #000;
  outline: 2px solid #444;
}