JSFiddle - React, Tailwind, and code Playground

HTML

<div id="left" class="horizontal">hello</div>
<div id="right" class="horizontal">world</div>

CSS

* {
    padding:0;
    margin:0;
    border:0;
    border-spacing:0;
    box-sizing: border-box;
    -moz-box-sizing: border-box;
}
html {
    height:100%;
}
body {
    height:100%;
}
#left {
    background-color: red;
    width:20%;
    height:100%;
}
#right {
    background-color: green;
    width:80%;
    height:100%;
}
.horizontal {
    display: inline-block;
}