Same as for illustrations, I can provide you different styles of book covers, both for e-books and print. Here is a presentation (sorry it is not in English, but it is very easy to understand): https://www.slideshare.net/artabella/coperte?qid=5203eb38-5b03-49f2-8f4e-dd0d46ff3275&v=&b=&from_search=2