JSFiddle - React, Tailwind, and code Playground

HTML

<div class="progressbar">
    <div class="buffer"></div>
</div>

CSS

.progressbar { height: 15px; width: 100px; border-radius: 5px; margin: 50px; background: black; }
.buffer { width: 25px; height: 15px; background: #999999; }