[Question] Migration guide: moving from v. 0.X to v. 1.X

Congratulations on v. 1.0 release! I found out a lot of things changed under the hood, but there are also some breaking changes, which are observable from the outside. For example, some CSS classes are gone now and therefore styling based on it have been broken.

Would you kindly provide some migration guide/notes about this and other breaking changes?