add a new stylesheet tag to the head

addStyle.js

addStyle = function( css ) {
	var styleEl = document.createElement( 'style' );
	styleEl.rel = 'stylesheet';
	// overwrite the stylesheet if it already exist...
	if ( styleEl.styleSheet ) { // IE
		styleEl.styleSheet.cssText = css;
	} else { // !IE
		styleEl.appendChild( document.createTextNode( css ) );
	}
	// attach the stylesheet to the page
	document.head.appendChild( styleEl );
};