html, body {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    overflow: hidden;
}

canvas {
  display: block;
  position: fixed; /* or absolute with top/left 0 */
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  touch-action: none; /* prevent browser gestures overriding */
}