JSFiddle - React, Tailwind, and code Playground

HTML

<div class="white">
    <div class="black"> </div>
</div>

CSS

body {
    background: blue;
}

.white {
    background: white;
    width: 500px;
    height: 250px;
    margin: 0 auto;
}

.black {
    background: grey;
    width: 30%;
    float: left;
    height: 100%;
}