JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
    <div class="columnA"></div>
    <div class="columnB"></div>
</div>

CSS

.columnA{height:100%; width:50px; background-color:#FF0000; float:left;}
.columnB{height:100%; width:50px; background-color:#00FF00; float:right;}
.parent{width:100px; height: 300px; outline:1px solid black; float: left;}