Cross-browser method for injecting passed CSS into the document

writeStyle.js

function writeStyle(rules){
	var head = document.getElementsByTagName('head')[0],
		el = this.el || document.createElement('style'),
		rules = rules || '';

	if(!this.el) 
		el.type = 'text/css';

	if(el.styleSheet){
		el.styleSheet.cssText = rules;
	}
	else{
		$(el).empty()
		el.appendChild(document.createTextNode(rules))
	};

	if(!this.el) 
		head.appendChild(el);

	this.el = el;
};