Background Transparency in Microsoft Expression Blend 4

I am making an app开发者_开发问答lication interface using Expression Blend 4. I want to remove the default title bar and main window to make the entire interface myself. I have managed to remove the title bar, but the white space at the back is still there. How can I remove this, or am I doing it wrong in general. For the record, I set AllowTransparency to true in order to remove the title bar in the first place. Thanks.

WindowStyle="None" AllowsTransparency="True" Opacity="0.8"

Set these 3 properties