JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://ajax.microsoft.com/ajax/jquery.validate/1.7/jquery.validate.js"></script>
<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.2/themes/ui-lightness/jquery-ui.css">
<ul>
    <li>first</li>
    <li>second</li>
    <li>third</li>
    <li>fourth</li>
    <li class='Last'>fifth</li>
</ul>

CSS

li {
    float: left;
    padding: 20px;
    list-style-type: none;
}

JavaScript

var left = $('ul li.Last').offset().left;

alert( left );