Have you looked at the file CHANGELOG.html in the docs folder of the download?
David Remember: You only know what you know and - you don't know what you don't know! My CDB Contributions | How to install an extension I will not be accepting translations for any of my extensions in Github - please post any translations in the appropriate topic. No support requests via PM or email as they will be ignored
Given the helpful answers (and no, I don't know either), just grab a tool like WinMerge (assuming you're on Windows) and you can easily compare the RC1 and RC2 CSS files yourself.