Dark Mode: update md_colors.css

These variables are used in various places, but I'm mainly updating
because bookmarks and history load this stylesheet remotely and use the
--md-* vars for their loading shells.

R=aee@chromium.org
BUG=883049

Change-Id: I161746c93268d82987f6a14d885180017678c804
Reviewed-on: https://chromium-review.googlesource.com/c/1378565
Reviewed-by: Esmael El-Moslimany <aee@chromium.org>
Commit-Queue: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619096}
1 file changed