Keeping formats consistent with main page

I have a quick question that may be more complicated to explain to me than to others because I have absolutely no PHP experience whatsoever. I'm an HTML and CSS guy, but any help with this would be greatly appreciated. Here is the site: newdust.com

Notice the black striped background of the body, and the blue striped background in the container where the top advertisement resides. If you click on any of the tags on the left sidebar, click any of the months under the archive, or even go to the next page of posts, those two formats disappear. I've read around and it appears that this is a PHP issue regarding the way these particular sections of the blog are rendered, but when I view the source of any of these pages I can see the CSS that I entered into the main stylesheet that should make it to where they follow suit with the main page. In other words, to a purely HTML/CSS guy like myself, what I see happening in the source code isn't happening on the live page. So I'm a bit stumped at this point. All signs point to PHP. Any ideas?