You can find out the classes and id of any object using one of the add-ins for Firefox (or IE I suppose.) In this case I see that the featured products on the main page are in the id featuredProducts and the class centerBoxContentsFeatured. You can add (if it's not there now) or modify (if it is) the style definitions for either of those in your stylesheet, persumably without affecting the styling of any text not associated with featured products.

Similarly the Specials are in id specialsDefault and class centerBoxContentsSpecials.

If, however, you were to change the style of the centerBoxWrapper class which holds both of the above you would affect many more things than just the Specials and Featured Products.

Those Firefox add-ins are your friend when trying to style something as complicated as a Zen Cart site.

Rob