JSFiddle - React, Tailwind, and code Playground

by Aides

HTML

<div class="scrollable">

</div>
<div class="fixed">

</div>

CSS

html, body
{
  overflow: hidden;
  width: 100%;
  height: 100%;
}

.scrollable
{
  overflow-y: auto;
  height: 80%;
  width: 100%;
}

.fixed
{
  height: 5px;
  position: fixed;
  left: 0px;
  right: 0px;
  background-color: red;
}

JavaScript

for(var i = 0; i < 500; i++)
{
	$('.scrollable').append('<div id="'+i+'">Lorem ipsum</div>'); 
}

console.log($('.scrollable'))
window.setInterval(function()
{
	var anchor =$('#200').closest('.scrollable') 
	$('.fixed').css('top', anchor.offset().top);
	console.log(anchor.offset().top);
}, 10);