Update our dropdown highlighting

Proposed here by @cperessini: https://gitlab.com/gitlab-org/gitlab-ce/issues/28410#note_24269943

I created this issue as the design was not yet implemented

Proposal

Currently:

proposed:

Value

Imo this simplifies the UI for the better and is clearer

Related issues

https://gitlab.com/gitlab-org/gitlab-ce/issues/28410

cc: @annabeldunstone @tauriedavis @pedroms @cperessini @alfredo1

mentioned in issue #28410 (closed)

@dimitrieh I created #28921 (moved) a few days ago so we can identify dropdowns where this new style may result problematic. I mentioned it in the MR, but not in the original issue, sorry!

closed

Closing as duplicate of #28921 (moved)