Sprinkle some child selectors around in BookletLayout styles

PanelLayouts are commonly nested, and we don't want random
PanelLayouts getting weird width and padding treatments
just because they're inside another PanelLayout
that's inside a BookletLayout.

Bug: T78548
Change-Id: Ie0ddf21b5ab49f6d07f8e925c87b9b8aee1d8fa2
Merge "Sprinkle some child selectors around in BookletLayout styles"