JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="left">left one</div>
    <div id="right">right one</div>
</div>

CSS

#container {
    position: relative;
    height: 150px;
}

#left, #right {
    position: absolute;
    top: 0px; bottom: 0px;
}

#left {
    left: 0px; width: 300px;
    background: red;
}

#right {
    left: 300px; right: 0px;    
    background: green;
}