JSFiddle - React, Tailwind, and code Playground

HTML

<div id="content">
    <div id="mainbox">
        <h1>title</h1>
        <h3>title</h3>
        <p>text</p>
        <ul>
            <li>Vivamus vestibulum nulla nec ante.</li>
            <li>Praesent placerat risus quis eros.</li>
        </ul>
    </div>
    <div id="relatedbox">
        <h1>Related</h1>
        <p>text</p>
    </div>
</div>

CSS

#content {
    height: 200px;
    width:300px;
    margin-left: auto;
    margin-right: auto;
    background:red;
}


    #mainbox{
    margin:0 auto;
    background:yellow;
    width:100px;
}
#content #relatedbox {
    width: 200px;
    font-size: 10pt;
    background-color: white;
    margin: 1em 0.5em 1em;
    border: 3px solid #00824c;
    float: left;
}