ument.documentElement;

  /* View in fullscreen */
  function openFullscreen() {
    if (docElem.requestFullscreen) {
      docElem.requestFullscreen();
    } else if (docElem.mozRequestFullScreen) { /* Firefox */
      docElem.mozRequestFullScreen();
    } else if (docElem.webkitRequestFullscreen) { /* Chrome, Safari and Opera */
      docElem.webkitRequestFullscreen();
    } else if (docElem.msRequestFullscreen) { /* IE/Edge */
      docElem.msRequestFullscreen();
    }
  }

  /* Close fullscreen */
  fun