JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="object">asd</div>
</div>

CSS

#container { width: 400px; background: #f00; padding: 2px; }
#object { width: 200px; background: #000; color: #fff; }

JavaScript

$('#object').width($('#object').parent().width());