The following example displays the gpUrlLoader Class with an option to load a CSS file. Add the event listener, then call the init method with the url and the load type.
var ldr:gpUrlLoader = new gpUrlLoader();
ldr.addEventListener(Event.COMPLETE, sheetLoaded);
ldr.init('styles.css', 'stylesheet');
function sheetLoaded(event:Event):void {
var mycss:StyleSheet = ldr.getStyleSheet();
}
For documentation about the gpUrlLoader AS3 Class, view the blog post.