JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="bar"></div>
</div>

CSS

#container {
    border: 2px solid black;
    overflow: hidden;
}

#bar {
    position: relative;
    left: -50%;
    width: 100px;
    height: 40px;
    background: #aaa;
}

JavaScript

$('#bar').animate({left: '0%'}, 1000);