Unify hover/selected background states.

Selected = blue
Hover = grey

For use in rects selection, active/hover timeline states, and node hover/selected states.

Figma screenshot: https://screenshot.googleplex.com/6ykZErr6nbCrwmG

Final screencast: https://screencast.googleplex.com/cast/NDkwMDE0MTE4NTEwNTkyMHw1YWVkZDEwYy0xNg

Bug: 360336024
Test: n/a

Change-Id: Ice0b4beaefbe4a36917094229be5a71ef1e128b7
5 files changed