JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    width:300px;
    height:200px;
    overflow:hidden;
    position:relative;
    left:100px;
    top:50px;
}
div:before {
    content:'';
    position:absolute;
    top:0;
    left:-100px; /* should be equal to height */
    height:100%;
    width:200px;/* should be equal to height */
    border-radius:50%;
    box-shadow:0 0 0 1000px red;    
}
body {
    background:url(http://lorempixel.com/800/600);
}