JSFiddle - React, Tailwind, and code Playground

HTML

<div id="bred">
    <div id="tupo">&nbsp;</div>
</div>

CSS

body{
    background:#e6e6e6;
}

#bred{
    width:100%;
    height:100px;
    background:#808080;
}

#tupo{
    width:100%;
    height:10px;
    background:#e6e6e6;
    border-radius:0 0 50% 50%;
}