Theme Builder

Hey guys, I'm new to the whole themebuilder and confluence thing. But I have to use CSS to change my company's wiki site, particularly, I have to use the themebuilder's custom css to change the look of the site. I am pretty new to this thing. But I think I have a relatively good understanding of CSS. But I just don't know what to name my styles and ID's because I don't know where they go. Does confluence use a group of ID's and styles somewhere? And if they do, where can I find them? I'm just sitting here unsure of what to type in. Based on the tutorials I know that .breadcrumbs controls the text in the breadcrumbs area, but I have no idea what the other names are. Is there a list of these Styles and ID's somewhere? Please help!

Thanks so much.