JSFiddle - React, Tailwind, and code Playground

HTML

<div id='container' class="clearfix">
    <div id='left'>Left content</div>
    <div id='right'>Right content</div>
</div>

CSS

#container {
    border:solid 3px red;
}

#left {
    float: left;
    background-color: lightblue;
    height: 300px;
}

#right {
    float: left;
    background-color: coral;
    height: 300px;
}

.clearfix:before,
.clearfix:after {
    content: " "; 
    display: table; 
}

.clearfix:after {
    clear: both;
}