I tremble to enter this battle of formatting giants, but note that (as was said in another thread) html formatting is a matter of pairs. If you have a style in the style sheet, it won't be used unless the body of the book refers to that style; contrawise, there's no point calling for a class in the body of the book unless there's a matching style in the style sheet.
Personally, I'm with the
<p> faction. You are welcome to borrow or modify my style sheet from
http://notjohnkdp.blogspot.com/2013/...yle-sheet.html