css - Sharepoint Prediefined DIVの不透明度を設定するにはどうすればよいですか？

Question

As mentioned in title, I am not able to set opacity.
I tried using rgba(0,0,0,0.5) - not working.
also tried opacity:0.6; still not working.

Sharepoint 2010、IE9、SharepointDesigner2010を使用しています