How to change inbox background?

I have applied every other possible background packs out there to my game. It feels great but that one thing annoys me: I can't have any background images for inbox screen where we read messages etc. Remember in CM 03/04 we had different backgrounds in inbox? I want to make that one for FM 23. Is it possible to make already existing backgrounds to be shown in inbox? If not, how can I make a new folder of images spesifically for inbox screen?

I am talking about this.

But my current inbox is like this.
 

Note: I use Zealand skin 1.0

this is file inbox item.xml, it currently uses classes main_contrast_box and inner_contrast_box_no_margin for containers. they are opaque. 
the easiest way to achieve transparency is simply to use a fake appearance. for example like this class="inner_contrast_box_no_margin" appearance="fake/appearance/for/transparency"

Can you explain in a more simple way? I don't understand where is the xml file or where are these code lines at. What I should do exactly?