change font on calibre to iPad

iPad have iBooks app to read ebook. This app content 5-6 font pre-installed to choice, but if I change font, on all ebook I have this changes!
I want change font on one my ePub with calibre on stylesheet css file and after read this ebook on my iPad (mini)
I've try with font-family (font name) but I see difference on calibre but not on iPad! All font is the same! I've try with name of windows font and with Apple font, but I see this difference only on calibre, after on my iPad not!
How to change family font to read on my iPad?