CSS Specificity

I think this article does the topic much better justice than I ever could, but here is my two cents. http://www.smashingmagazine.com/2007/07/27/css-specificity-things-you-should-know/

Specificity allows you to specify which properties you wish to apply to which elements. Basically, there are two parts to CSS rules. There's the part of what you want it to look like (for example, background: green;) as well as what you want that look to apply to (for example, h1, .nav, #wrapper, etc.). Specificity uses a set of rules outlined in the article above to determine which elements get the looks you want applied to them.

A big part of specificity is the order in which the styles are applied. All else equal, if you accidentally apply two styles to the same element, then the last style wins. For example, consider the code:

div {
   background: red;
}

div {
   background: green;
}

In this case, the background of the divs will be green because this rule is applied second. You can get around this with the !important flag (background: red !important; will make it red) but be careful when using it, and I try to avoid it. Here is more detail on CSS tricks as well: http://css-tricks.com/specifics-on-css-specificity/

Hope that helps! Let me know if you have further questions.

Smiles :) Laura