JSFiddle - React, Tailwind, and code Playground

HTML

<div></div>

CSS

div {
    width: 250px;
    height: 250px;
    margin: 10px;
    background: #448CCB;
}
div:before {
    content:" ";
    background:white;
    display: block;
    width:250px;
    height: 125px;
    border-radius: 0 0 125px 125px;
}