How can I get a dialog that doesn't cover the custom title bar?

[PleaseDont]

Sometimes, we need put some actions on the custom title bar that remain unaffected by the dialog, now the dialog functions like a sheet/drawer. Although the dialog has a margin_top attribute, but it doesn't apply to the mask layer.
I'm considering whether it's feasible to take the mask layers out of the dialog and sheet into a standalone component. For instance, we could sometimes add a loading indicator on the mask layer to signal that something is being loaded.

[huacnlee]

#1789