JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

#shape {
    width:250px;
    height:250px;
    background:#448ccb;
    position:relative;
}

#shape:before {
    content:" ";
    position:absolute;
    width:250px;
    height:250px;
    background:#fff;
    left:0; top:-50%;
    border-radius:50%;
}