Butona tuş atama

 <div id="expand-icon">
        <i class="fas fa-expand" title="fullscreen mode" onclick="openFullscreen();"></i>
      </div>
      <script>
        var elem = document.getElementById("expand-icon");
        function openFullscreen() {
          if (elem.requestFullscreen) {
            elem.requestFullscreen();
          } else if (elem.webkitRequestFullscreen) {
            elem.webkitRequestFullscreen();
          } else if (elem.msRequestFullscreen) {
            elem.msRequestFullscreen();
          }
        }
        </script>

function toggleFullScreen() {
  var doc = window.document;
  var docEl = doc.documentElement;

  var requestFullScreen = docEl.requestFullscreen || docEl.mozRequestFullScreen || docEl.webkitRequestFullScreen || docEl.msRequestFullscreen;
  var cancelFullScreen = doc.exitFullscreen || doc.mozCancelFullScreen || doc.webkitExitFullscreen || doc.msExitFullscreen;

  if(!doc.fullscreenElement && !doc.mozFullScreenElement && !doc.webkitFullscreenElement && !doc.msFullscreenElement) {
    requestFullScreen.call(docEl);
  }
  else {
    cancelFullScreen.call(doc);
  }
}