Find a book you like in the MR library. Three Men in a Boat is a good choice and look at any special formatting you like. Switch to code view and see what they used to get it. Then switch over to the stylesheet view for the code you just saw. Then go to w3schools.com for a further explanation if you need one.
For many books you don't need extra fonts at all. The plainest of books won't need much in the way of a stylesheet either. But as you get more familiar with epubs you will likely want to be able to make chapter titles nicer looking etc.
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