Success.html

<iframe id="bloxorzIframe" loading='eager' src='https://www.coolmathgames.com/0-bloxorz' hidden></iframe>
<button id="bloxorzButton">Bloxorz</button>
<script>
function bloxorsButton() {
alert("bloxorsclicked");
  var bloxorziframe = document.getElementById("bloxorsIframe");
  bloxorziframe.removeAttribute("hidden");
}
  document.getElementById('bloxorzButton').onclick = function() {
    alert("button was clicked");
    var bloxorziframe = document.getElementById("bloxorzIframe");
    bloxorziframe.removeAttribute("hidden");
    bloxorzFullscreen();
}
  var elem = document.getElementById("bloxorzIframe");
function bloxorzFullscreen() {
  if (elem.requestFullscreen) {
    elem.requestFullscreen();
  } else if (elem.webkitRequestFullscreen) { /* Safari */
    elem.webkitRequestFullscreen();
  } else if (elem.msRequestFullscreen) { /* IE11 */
    elem.msRequestFullscreen();
  }
}
</script>