How to make page or article backgrounds transparent

Hi, I would like to have a transparent background for the pages and articles, in order to let the body background beeing visible.

I didn't find in the style.css the lines to change...

Same question for the comments boxes. I don't want the black background, but I don't find where to change it.

Big thanks for your help.

Regards,

Guito

I find it !

This black color is not html color... but an image in the images/content folder.

I'm happy. :)