s|Alert{} in css

[Frank Dahmen]

throws

Warning: Cannot resolve namespace qualified type 'Alert' in CSS selector 
'Alert'

how can i set skinclass for spark alerts globally?

or how can i get  a new instance and show it?

var alert:Alert=new Alert();
alert.skinClass="alertSkin";
alert.show(.....);    <- does not work, static mehod

thanks