Diagnostics: Change the keyboard key color to match the specs

Change the tested state color in both normal and dark mode.Change the
border color in the pressed state to match the background color. Change
the variable name from foreground to text.

specs:
go/input-diagnostics-spec

Screenshots:
http://screen/7tVKWG3fFgngnEN
http://screen/Ae9GJ6nFPMydDmZ
http://screen/BKWwRJ363wuqTPa
http://screen/8wZLCApGSFsGpdW

Bug: b/207089601
Change-Id: Idfe46d060d2eee84abfad015a12c7d9dc4f94e94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4050002
Commit-Queue: Michael Checo <michaelcheco@google.com>
Reviewed-by: Michael Checo <michaelcheco@google.com>
Auto-Submit: Danny Wang <wangdanny@google.com>
Commit-Queue: Danny Wang <wangdanny@google.com>
Cr-Commit-Position: refs/heads/main@{#1076318}