@cybmole,
I also have found that Moon+ is quite poor at honouring internal css. Mantano, PocketBook and UBReader are much better in this respect. However, I'm not sure which, if any, of these will run on the not-quite-Android devices of Kobo and Kindle. PocketBook is free, UBReader has a free and a Pro version, Mantano has Lite (free), Essentials and Premium.
If you've got any patience left
maybe try one of them. They all have their pros and cons.
ETA: It's not just css that Moon+ fails to render correctly, it's also basic tags such as <blockquote> , <pre>, <ol>, <li> and I've also had problems with books that use <div ...> (instead of <p ...>) for their standard paragraphs.