* [WIP] BAB theme

* [WIP] BAB theme

* Update goldens

* Extract helper function in tests

* Update Goldens version

* Add tests

* [WIP] Hans first round comments

* Added test

* Added docs

* Hans second round comments

* Fixed analyzer error

* Hans third round comments

* ambient

* Change [BottomAppBarTheme.of] to static

* Final doc change