Hi all! 
In upgrading my app to App Bridge 4.x, and came across an interesting styling inconsistency when styling modals. Pre 4.x, modals with warning messages were styled like this:
Notice the slightly transparent yellow wrapping around the warning message. This uses a Polaris Banner within a Modal.
With App Bridge 4.x new Modal component, the modal with a warning banner now looks like this:
This example shows a regular Polaris Banner inside the App Bridge 4.x Modal.
Was styling for App Bridge 4.x modals overlooked? Or is this designed as intended? A potential workaround would be style the App Bridge 4.x Modal using Polaris components like Box, BlockStack, and Badge to match and App Bridge 3.x modal.
Any suggestions/feedback are most welcome.