You can check easily what CSS styles are coming from which CSS files by using Firebug tool. Just select HTML element using "Inspect" button and you'll see the list of applied styles.
I check it was overwrited by Richfaces CSS, because page always always import Richfaces CSS into last one. How can I reverse it and overwrite Richfaces CSS?
How do you include your CSS: embedded inline by STYLE tag, in external file using LINK or using a4j:loadStyle?