You changed threads, are you trying to confuse me?
As I said previously,
delete the
font-family statements. On a Kobo, font-family:serif will give you it's default font (some kind of Georgia). This is not the same as on a Sony where font-family:serif in the CSS was equivalent to no font-family at all.
...And try to relax a bit and enjoy the journey
I'm around all evening if you need specific help with Kobo vs Sony CSS issues. Go to PM if you prefer.