JSFiddle - React, Tailwind, and code Playground

HTML

Webkit 
<div id="container">
    <div id="margined">This has an auto margin!</div>
</div>

CSS

#container{
    position:relative;
    width:500px;   
}

#margined{
    margin:0 auto;
    width:250px;    
}

JavaScript

alert('Margined has a position( ).left of ' + $('#margined').position().left)