KF8 (.azw3) supports basically anything that EPUB does. Since it is essentially EPUB but wrapped in a mobipocket database instead of a ZIP container, it retains a lot more formatting source code, too -- you'll notice in MOBI-to-EPUB conversions a lot of really messy html including heavy use of spans.
This is because MOBI does not support CSS at all, although a limited subset can be translated into plain HTML.
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