JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://code.jquery.com/jquery-2.0.1.js"></script>
<body>
	<div id="container">
		<div id="box">
			<p>some text</p>
		</div>
	</div>
</body>

CSS

#container {width:100%;}
#box {border:1px solid black; margin:0 auto; box-sizing:border-box;}

JavaScript

var $ = jQuery.noConflict();
$(document).ready(function() {
    $('#box').width('10em'); // width should be 10em, but jquery set it to 12em
});