JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap"></div>

CSS

.wrap{
width:300px;
height:300px;
margin:0 auto;
position:relative;
background:#fff;
border:1px solid #ccc;
}

.wrap:before{
content:"";
position:absolute;
top:20px;
bottom:20px;
width:100%;
border-radius:80px;
box-shadow:0px 0px 30px 6px #ccc;
z-index:-1;
}