    /* Get the documentElement (<html>) to display the page in fullscreen */
    var elem = document.documentElement;
    
    /* View in fullscreen */
    function openFullscreen() { 
      if (elem.requestFullscreen) {
        elem.requestFullscreen();
      } else if (elem.mozRequestFullScreen) { /* Firefox */
        elem.mozRequestFullScreen();
      } else if (elem.webkitRequestFullscreen) { /* Chrome, Safari and Opera */
        elem.webkitRequestFullscreen();
      } else if (elem.msRequestFullscreen) { /* IE/Edge */
        elem.msRequestFullscreen();
      }
    }
    function closeFullscreen() {
  if (document.exitFullscreen) {
    document.exitFullscreen();
  } else if (document.mozCancelFullScreen) { /* Firefox */
    document.mozCancelFullScreen();
  } else if (document.webkitExitFullscreen) { /* Chrome, Safari and Opera */
    document.webkitExitFullscreen();
  } else if (document.msExitFullscreen) { /* IE/Edge */
    document.msExitFullscreen();
  }
  
}