JSFiddle - React, Tailwind, and code Playground

HTML

<div class="halfOval"></div>

CSS

.halfOval { 
    background-color: #a0C580;
    width: 400px;
    height: 100px;
    margin: 100px auto 0px;
    border-radius: 50% 50% 0 0/ 100% 100% 0px 0px;
}