JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.back { 
    height: 200px;
    background-color: #000000;
     position: relative;
}
.halfOval { 
    background-color: #a0C580;
    width: 850px;
    height: 100px;
    margin: 100px auto 0px;
    border-radius: 50% 50% 0 0/ 100% 100% 0px 0px;
     position: absolute;
    bottom: 0;
    left: 0;
}