Dark Mode: fix primary/secondary button shadow colors

The spec was a little hard to read, but I think this is correct.

Screenshots: https://imgur.com/a/SqOdxgO
Specs: https://docs.google.com/presentation/d/1kJoBzf_HGYK-_FAJPAjD67TW8224dCPLA6dAhlDmysk/edit?ts=5c363f50#slide=id.g471d243f08_0_869

R=dpapad@chromium.org
BUG=883049

Change-Id: Ie377f7c4ba52a3a4540497b15b8a7bb8ad67853a
Reviewed-on: https://chromium-review.googlesource.com/c/1426157
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624887}
1 file changed