Update drop target styling based for BC.

Spec: https://docs.google.com/presentation/d/1UxdDh8EFhPbdRWRwzjbpgL-j02ew4Ew3eG3XBCeoYdo/edit#slide=id.vXfwHn8

Demo: https://drive.google.com/file/d/1ZIa3Dgo85vdVkfPm7aGJDyctZQR_c8Xx/view?usp=sharing

Test: manual
Bug: 184713740
Change-Id: I17dbbf1f7bbc40939cfc0fedb506a35f39ecc2e3
10 files changed