JSFiddle - React, Tailwind, and code Playground

HTML

<div id="oval-shape"></div>

CSS

#oval-shape {
    width: 200px;
    height: 100px;
    background: blue;
    -moz-border-radius: 100px / 50px;
    -webkit-border-radius: 100px / 50px;
    border-radius: 100px / 50px;
}