[Settings containment] Add custom background color to Safety check

Before: https://screenshot.googleplex.com/9LJ7oj9ju99h5zH.png
After: https://screenshot.googleplex.com/5oM7XEhspGCxh5K.png

Bug: 433576895, 439725777

Change-Id: Ida611c0b494fc139381eaf2d6103bd1caae8afd3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6914515
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Gazal Agarwal <agazal@google.com>
Auto-Submit: Gazal Agarwal <agazal@google.com>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1511828}