Define textDecoration, a noninheriting property, to the global selector
<?xml version="1.0"?> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> <mx:Style> global { extDecoration: underline; } </mx:Style> <mx:Button id="myButton" label="Click Here"/> <mx:Label id="myLabel" text="This is a label"/> </mx:Application>