Remember there's a difference between the element id and class attributes. id's are usually only given to items on a page which will only occur once (eg. a header or footer) since an id can only be used once in html. classes are given to everything else. In css, you reference an id by #id_name, while with a class its .class_name. So in this case, category is a class, so to style it, you should use something like:

p elements are block elements so it already spans the entire width. You can put a border-bottom/top on it to make it divide things up.

They are definition lists

Adrian