Merge "UX polish: preview size, toolbar color." into tm-qpr-dev am: ec4562f472 am: c2730034e3

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

Change-Id: I9220a261d7a7a75d9d8f26d923883a3c3d10a9ce
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>