JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="inner">
    </div>
</div>

CSS

#container
{
    height:400px;
    width:400px;
    border:1px black solid;
}

#inner
{
    height:200px;
    width:200px;
    background:black;
    border-radius: 100px;
    -moz-border-radius: 100px;
    -webkit-border-radius: 100px;
    margin-left:25%;
    margin-top:25%;
}