JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="first">FIRST</div>
    <div id="second">SECOND</div>
</div>

CSS

#container {
    width: 500px;    
    display: flex;
}

#container > div {
    height: 300px;
    font: bold 3em Futura;
    text-align: center;
    line-height: 100px;
}

#container > #first {
    width: 200px;    
    background-color: #ccf;
}

#container > #second {
    flex-grow: 1;
    background-color: #fcc;
}