JSFiddle - React, Tailwind, and code Playground

HTML

<header></header>
<section>
    <div id="content"></div>
    <div id="side"></div>
    
    <div style="clear: right;"></div>
</section>
<footer></footer>

CSS

header, div, section, footer{ display: block; }
header{
    background-color: #1361aa;
    width: 500px;
    margin: 0 auto;
    height: 80px;
}
section{
    width: 500px;
    margin: 0 auto;
}
section > #content{
    float: right;
    width: 350px;
    height: 90px;
    background-color: #ff0000;
}
section > #side{
    width: 150px;
    height: 90px;
    background-color: yellow;
}
footer{
    margin: 0 auto;
    width: 500px;
    height: 40px;
    background-color: #000;
}