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Regarding CSS, neither ePub 2 or ePub 3 supports neither CSS2 or CSS3. They both support some subset of them with some additional properties.
But "support" here simply means that compliant readers are required to know some properties and values (not always to do anything useful with them). Unfortunately, no reader actually supports what they are required too. And then any reader is allowed to support additional properties.
Since CSS is designed to ignore unknown properties, this means you should be able to use whatever you want in the CSS (as long as it's syntactically correct), but can never be sure of the effect it will have on a reader without trying. I mean, the resulting ePub will be valid, but may not work exactly as intended.
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