WebUI Dark Mode, Settings: fix some (kinda-)shared styles

R=dpapad@chromium.org
BUG=926658

Change-Id: Ie366c11f284e5b780a7818708488e33feb080f6c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1509612
Auto-Submit: Dan Beam (slow; perfing) <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Dan Beam (slow; perfing) <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638896}
2 files changed