Hi,
More than the data, all the module is build on the fly. Then, if you look inside Account.ascx, you will find just a structure with links (My Cart, Order History) on the top and a placeholder. When user click on My Cart, the CustomerCart.ascx control is loaded. This one control the button to display (Loggin, Checkout, Add Item) and load the CartDetail.ascx for display the cart content. As you can see, it's a little bit complex to explain. For this reason, we choose to use more "logical" name related to the sub modules for the css, because generaly a designer is NOT a developer.
Concerning the css, there is only one css file referenced inside the store: template.css. This file is responsible to load other css files (Common.css, SkinObjects.css, MiniCart.css, Cart.css, ...). Because the use of this structure, you can change everything inside the css even the file names. The only requirement is to have template.css in the Templates folder. This offer the full control to the designer. Then, if you don't like the css file name and how the classes are distributed inside, you can change it!
Because the Store module is a work in progress, sometimes you will find empty classes definitions as "Store-Account-BtnTD..." inside Common.css. On the other hand, you can find a class name defined inside an ascx without corresponding class definition in the css files, this is the case for DIV.Store-Account-Entity. Then, you can define the style for this class where you want in the css files!
Gilles