JSFiddle - React, Tailwind, and code Playground

HTML

<div class="line"></div>
<div class="line"></div>
<div></div>

CSS

div{
position:relative;
width:200px;
height:100px;
background:#ccc;
border:1px solid #888;    
margin-bottom:10px;
}

.line:after{
position:absolute;
content:'';
width:inherit;
bottom:-7px;
border:1px solid #000;
}