CSS Selectors & Rule-Sets

I have never actually taken the time out to sit down and learn the structure of the CSS language, it is something I have just picked up and used what I need, when I need. Therefore, reading up on CSS Selectors and Rule-Sets has helped to pull the pieces together and discovering the applied rules section in the Visual Studio CSS Properties dialog should hopefully same me a lot of time racking my brains to figure out why that style I have just added is not being applied!