body {
  background: #000;
}

canvas {
  height: 480px;
  position: absolute;
  left: 50%; top: 50%;;
  margin: -240px 0 0 0;
  border: 1px dashed #666;
}

#world {
  width: 640px;
  margin-left: -215px;
}

#menu {
  width: 200px;
  margin-left: -425px;
}