JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

html, body {
  height: 100%;
}

#a {
    width: 15%;
    height: 10%;
    background: red;
    display: inline-block;
}

#b {
    width: 15%;
    height: 10%;
    background: black;
    display: inline-block;
}