At our June meeting, we talked about the "cascade" in cascading style sheets. We looked at the different ways of applying styles to a page and how the cascade determines which of conflicting styles is applied to an element.
We reviewed browser default styles and how a user can change those default settings. We then looked at inline, embedded, linked, and imported styles. Where styles conflict, the more specific style sheet will prevail, though the priorities can be reversed by adding "!important" to a style declaration.
I posted a test file at the Sample Pages section of the website (look at the bottom of the page). You can download a zipped folder that contains the page and three style sheets. Open the page in an editor to play with the style definitions and understand how the cascade works. For more help, try HTML Dog which has a number of tutorials.