JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrap">
    <div class="shadow"></div>
</div>
<div class="wrap">
    <div class="shadow"></div>
</div>
<div class="wrap">
    <div class="shadow"></div>
</div>

CSS

body{
margin:0;
padding:0;
background:#ccc;
}
.wrap { width: 100%; height: 200px; background: red; float: left; position: relative; margin: 10px 0;}
.wrap .shadow { 
    position: absolute; 
    height: 10px;
    background: blue; 
    bottom: -10px; 
    width: 100%;
}