JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outside">hey</div>
<div id="inside">dsd
<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
</div>

CSS

#inside{
 	background-color:#f8f8f8;
	position: absolute;
	top:0;
	left:20%;
	width:60%;
	margin-top:35px;
	margin-bottom:35px;
	z-index:3;
	border-radius: 7px;
	box-shadow: 6px 6px 20px black;	
}


#outside{
	position: fixed;
	left:0;
	top:0;
	height: 100%;
	width: 100%;
	background-color: black;
	opacity:0.7;
	z-index:2;
	background-attachment:fixed;
}