JSFiddle - React, Tailwind, and code Playground

HTML

<div id="a">
    <div id="b"></div>
    <div id="c"></div>
</div>

CSS

#a {
    width: 400px;
    height: 200px;
    background: #000;
}
#b {
    float: left;
    width: 50%;
    height: 100%;
    background: #f00;
}
#c {
    float: left;
    width: 20%;
    height: 40%;
    background: #00f;
}