transparent scrollPane background

Hi there, there seems to be loads of threads about this, but none of the ones I came across helped me:
I'm using a scrollPane v2.0 component and I successfuly customized it (playing with the components assets on the library) and removed the border as well ("my_sp.setStyle("borderStyle", "none");") but couldn't find a way to get rid of the white background (I need to see what's underneath); it should be possible, isn't it?

Thanks for your help!