mainbody with no white background

Hi,

I want to have a semitransparent .png in the mainbody position of the template. However there is a white background when I publish something there. When I tried to remove the background it turned out to be the same div.box as the side modules.

How do I place a large semitransparent .png instead of the pre instaled header and without the white background?

i'll just add that I added transparent suffix but still had to change #gkContent background... and this removed the background from all articles.