[Woo POS] Animation to `Processing payment` has purple stripe effect

[joshheald]

Description

After tapping a card in POS, we animate to the purple Processing payment screen

This animation has a strange effect where the overall screen's background colour opacity increases through the animation, but the central block of content (full width) has 100% opacity throughout the animation. That makes it appear as though there's a stripe in the middle of the screen during the animation.

Ideally, both the content and the background should have the same opacity throughout the animation, so the screen feels like one thing.

[dangermattic]

🚫 Please add a type label (e.g. type: enhancement) and a feature label (e.g. feature: stats) to this issue.