JSFiddle - React, Tailwind, and code Playground
HTML
<div class="box">
</div>CSS
.box { width:400px; height: 600px; border:5px solid #dddddd; position: relative;overflow: hidden;}
.box:after { background:#dddddd; width:100px; height: 100px; border-radius: 50%; content:''; position: absolute; right:-50px; top: 20px; }