JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outer">
    <div id="inner"></div>
</div>

CSS

#outer {
    width: 400px;
    border: solid 1px green;
}
#inner {
    width: 20%;
    height: 100px;
    background: red;
}

JavaScript

$('#inner').animate({width: '100%'}, 500);