WebUI Dark Mode: update About page update checkmark/error icons

Screenshots: https://imgur.com/a/CoU73B4

R=hcarmona@chromium.org
BUG=926658

Change-Id: If741189597175b1068d7fcd4a8521b997a40a862
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1501792
Commit-Queue: Dan Beam <dbeam@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Reviewed-by: Hector Carmona <hcarmona@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637610}
1 file changed