index.css

body {
  background-color: #202020;
  color: #fff;

  /* Allow mouse dragging. */
  -moz-user-select: none;
  -ms-user-select: none;
  -o-user-select: none;
  -webkit-user-select: none;
  user-select: none;

  /* disable touch panning/zooming */
  -ms-touch-action: none;
  touch-action: none;

  /* Allow canvas to hit the edges of the browser viewport. */
  margin: 0;
}

#screen canvas {
  margin: auto;
  /* Hide the gap for font descenders. */
  display: block;
}