JSFiddle - React, Tailwind, and code Playground
HTML
<div class="background-size">
<div class="outside">
<div class="inside">
<p>
This div must go full "background-size" width. Help!
</p>
</div>
</div>
</div>CSS
.background-size {background-color: #424243; width: 100%; height: 50vh; }
.outside {background-color: #4286f4; height: 10vh; max-width: 500px; }
.inside { background-color: #ababab; width: 50%; height: 100%; margin: 0 auto;}