Please I would like to make a div disappear if it has been scrolled vertically up to 80% of it's total height. I tried using this javascript code but it didn't work.

<script>
        window.onscroll = function() {myFunction()};
        function myFunction() {
            var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) 
 / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
            if ( scrollpercent>0.8{
                document.getElementById("mega").style.display= "none";
            }
            else{
                document.getElementById("mega").style.display= "block";
                
            }
        }
    
 </script>

Please help me know what I am doing wrong.