Custom background image in Unity WebPlayer Loading Screen

Hi, I read the documentation about WebPlayer customization http://docs.unity3d.com/Manual/CustomizingtheUnityWebPlayerloadingscreen.html I customized logo and some other settings but now I need to apply a background image instead of background color.

I tried to apply some background-image style without success, then I tried to make logo-image bigger as WebPlayer and use it like a background but the result was horrible.

Html and Css are not my strong points and I'm starting to think it's impossible to add a simple background image. Isn't it?