Change swipe up onboarding color based on nav bar color

If the nav bar icons are dark, the onboarding content is
also dark on a white background. Otherwise the onboarding
content is white on a black background.

Also updated a couple of visuals:
- Added a divider to the top of onboarding
- Increased text size to 16sp
- Added ripple to dismiss "X"

Test: manual

Bug: 70180942
Change-Id: Ifc51143ba7e32015bc1519f9d79f9249849787a5