Merge "UX polish: preview size, toolbar color." into tm-qpr-dev am: ec4562f472

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/ThemePicker/+/21063820

Change-Id: I3e6fa1ad17979fd876ed75a9393478be345a1e53
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>