How to disable toggle full screen X button in ipad

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ASP.NET

If i changed the screen mode in full screen automatically will appear in close button, i need to disable the option please any one suggest

What I have tried:

document.getElementById("BtnFullscreen").addEventListener("click", function () {
                var
                    el = document.documentElement
             
                    , rfs = el.webkitRequestFullScreen;

                rfs.call(el);

                $("close").remove(); 
                return false;

            });
        }