Dark Mode: fix accidentally removed dependency

Certain shades of our Google palette are only in shared_vars_css.html,
not in paper-styles/color.html

https://crrev.com/c/1399512 made that faulty assumption.

This broke buttons on many pages (i.e. welcome, sign in dialog, etc.)

TBR=dpapad@chromium.org
BUG=883049,920540,920537

Change-Id: I7b019f90007612fb020b33535b79410447ca8666
Reviewed-on: https://chromium-review.googlesource.com/c/1405724
Reviewed-by: Dan Beam <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621921}
1 file changed