Hello everyone, I"m going to create a top navigation because for some reason I have to use absolute positioning. But when the scroll bar goes down, the navigation bar will flash very tired. The code is as follows:

< html >
< head >

<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<title></title>
<link rel="stylesheet" href="">
<style>
     body, html {
            padding:0;
            margin: 0;
            width: 100%;
            height: 100%;
            position: relative;
        }
  -sharptop {
            position: absolute;
            left:0;
            top:0;
            height: 20px;
            width: 100%;
            background-color: red;
        }
        -sharpbody {
            width: 100%;
            height: 150%;
            background-color: yellow;
        }
</style>

< / head >
< body >
< div id= "top" > < / div >
< div id= "body" > < / div >
< / body >

< script >
var doc = document;
var Dtop = doc.getElementById ("top");
var dBody = doc.getElementById (" body");

function getScrollTop () {

var scrollTop=0;
if(document.documentElement&&document.documentElement.scrollTop)
{
    scrollTop=document.documentElement.scrollTop;
}
else if(document.body)
{
    scrollTop=document.body.scrollTop;
}
return scrollTop;

}

window.addEventListener ("scroll", function (e) {

var e = window.event || e;
var scrollTop = getScrollTop();
Dtop.style.top = scrollTop + "px"

})

< / script >
< / html >

find a solution, thank you