Inheritance and Cascading in CSS
http://www.webdesignfromscratch.com/css-inheritance-cascade.cfm

Hunt, Ben
Web Design From Scratch
2006

Abstract:

This is a guide to help people learning CSS to understand how a browser works out what styles to apply to a particular element. As we saw in the introduction to CSS, there are lots of ways you can apply styles to a particular element. When more than one of these methods applies, how do you know which styles will be applied? Fortunately, these rules are quite simple, once you know them. This article tries to explain all. Of course, the best way really to learn this stuff is to try stuff out and see what happens.