Room sidebar search pill blur refinement

[dnisbetjones]

See comparison of the blur effect behind the search pill between Relay and iMessage. You can see that legibility is an issue. This could be solved by expanding the blur effect as iMessage does.

[subpop]

Messages.app still has a better blur effect than Relay, but what I'm seeing in Relay 0.4.3 right now looks better than your original screenshot.

I'll explore this more, but I have a feeling that it's the best we're going to get without implementing a custom header for the room list. The room list is currently relying on SwiftUI's .searchable view modifier to add a search bar automatically.