JSFiddle - React, Tailwind, and code Playground

HTML

<div class="black">
<div class="grey">
<div class="red">red</div>
<div class="blue">blue</div>
</div>
</div>

CSS

.black {
   width: 200px;
   height: 100px;
   background: black;
}

.grey {
   width: 180px;
   height: 100%;
   background: grey;
}

.red {
   width: 160px;
   height: 20px;
   background: red;
}

.blue {
   width: 140px;
   height: 100%;
   background: blue;
}