WebUI Dark Mode: fix offset, blur, and spread of ambient card shadows

R=dpapad@chromium.org
BUG=883049

Change-Id: Ib9385cef15b56c4b94babbd41d776d1b349fd6f5
Reviewed-on: https://chromium-review.googlesource.com/c/1444811
Commit-Queue: Dan Beam <dbeam@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Auto-Submit: Dan Beam <dbeam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#627311}
1 file changed