A graphic question

Hi

I am adjusting the Minimatica theme for another at http://øavisen.dk/ He wants to have background graphics on the homepage http://øavisen.dk/diverse/background.jpg

I have run into a problem, see here (the red arrow) http://øavisen.dk/diverse/screenshot1.png Can I change it so that the white triangle becomes transparant, so that the background graphics arrives instead of the white colour.

I have tried for 8 days to change the style.css. I cannot tell where I´m supposed to change it, so that the white triangle becomes transparant.

It’s only the white triangle wich has to be changed http://øavisen.dk/diverse/screenshot1.png Not any other places, e.g. when somebody answer a contribution http://øavisen.dk/diverse/screenshot2.png

Is there a solution to this problem?

Regards Carl