JSFiddle - React, Tailwind, and code Playground

HTML

<html>
	<head>
		<style>
			html, body {
				margin:0;
				padding:0;
			}
			#EL1 {
				height: 200px;
				background: red;
				position: fixed;
				width: 300px;
				top: 300px;
			}
			
			#EL2 {
				width: 400px;
				height: 40px;
				background: orange;
                cursor: pointer;
				position: relative;
			}
		</style>
		
		<script>
			window.onload = function() {
		    var block_c = document.getElementById('EL1');
			var block_d = document.getElementById('EL2');
				
if(block_c.style.display != 'none') {
	block_d.style.top = parseInt(window.getComputedStyle(block_c, null).top) + parseInt(window.getComputedStyle(block_c, null).height) + 'px';
}
			}
		</script>
	</head>
	<body>
		<div id='EL1'></div>
		
		
		<div id='EL2'></div>
	<body>
</html>