load CSS using JS

loadCSS.js

function loadCSS(href, options){
	'use strict';
	options = options || {};
	var styleSheet = document.createElement('link');
	var ref = options.before || document.getElementsByTagName('script')[0];
	styleSheet.media = 'not all';
	styleSheet.rel = 'stylesheet';
	styleSheet.href = href;
	styleSheet.onload = function () {
		styleSheet.onload = null; // only run once
		styleSheet.media = options.media || 'all';
		if (typeof(options.callback) === 'function') {
			options.callback();
		}
	};
	ref.parentNode.insertBefore(styleSheet, ref);
	return styleSheet;
}

Based on https://github.com/filamentgroup/loadcss