JSFiddle - React, Tailwind, and code Playground

HTML

<div class="a">
    <div class="b"></div>
    <div class="c"></div>
    <div class="clear"></div>
</div>

CSS

.b,.c{
    background-color: #444;
    border-left: 1px solid #666;
    border-right: 1px solid #000;
    width:50px;
    height:50px;
    float:left;
}
.clear{clear: both;}