JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    ASDF
</div>
<div class="clear"></div>
<div id="blue">*I have no content*</div>

CSS

#container{margin-left:auto;margin-right:auto;width:200px;}

.clear{clear:both;display:block;overflow:hidden;visibility:hidden;width:0;height:0;}

#blue{width:100%;background:blue;}