Different background on every page (but not child-pages)

I'm trying to give different pages different backgrounds. I've been searching for an answer and seem to have found one, but I can't get it to work.
Supposedly I can refer to different pages in my .CSS file by creating an extra class to the body section.
First I have to find out what the specific name for my page is. I read that using Firebug add-on for Firefox would help. Using this add-on I could define the page names. The next step was to alter my .CSS file like this:body .section-name-of-section-1 { background: Red; }body .section-name-of-section-2 { background: Green; }body .section-name-of-section-3 {background: Blue; }
But this doesn't work. What am I doing wrong?
Extra:
The website I am developing will have pages like 'About us' and 'Work'. These pages have child pages. With this I mean that from every page you can navigate to a different page. In example: in the 'About us' page you can navigate to different pages containing information about every employee. And in 'Work' you can navigate to every case the compagny worked on.
It would be very tiresome if I have to define every page in my .CSS file. And the people from said 'company' would have to add a line to the .CSS file when they finished a new case or hired a new employee. The whole reason of using a CMS system is to refrain from that.
Does anyone know a solution?