Trying to edit themes someone built for me

Someone built a few themes for me and I’m starting to become familiar with CSS but I’m not quite there yet. I’m currently having two problems:

1. I want the background of the page to be one color, and the central body area to be another. It looks like he has the body area set at a transparency, but I can’t find it in the code anywhere. The background and the body look to me like they’re set at two solid hex values and I can’t find an !important that overrides it. Help? There has to be something I’m not seeing.

2. He has another page with a background image at background-image: url(‘images/page_t.jpg’); but I can’t find this image in the media library. Is there a directory I’m missing?

Thanks for any help!