I was just going through a diff and figuring out just the differences.
If anyone cares heres a quick extract of the new classes. There’s a couple more declarations with a few minor differences but should not be an issue (hopefully).
I have not tried it, and would say that the class names don’t seem to match expected content, also inspecting a published post the markup seems to be the same. Anyway, some thought for the more daring :D.
@bob, is there a possibility of having the sass files for the current free themes, or even publish them in github. For the moment we only have this for the dev-starter theme. This would help a bit with making changes to existing themes.
Also have you considered adding support for css variables? This would make theming a little easier even without sass sources and browser support impact is pretty minimal, just a customary ie11 polyfill if you want to support it.