If translucent, the main content may slide behind it. Otherwise, the main content's top margin will be offset by its height.
The scaffold assumes the navigation bar will account for the MediaQuery top padding, also consume it if the navigation bar is opaque.
By default navigationBar disables text scaling to match the native iOS behavior. To override such behavior, wrap each of the navigationBar's components inside a MediaQuery with the desired TextScaler.
// TODO(xster): document its page transition animation when ready final ObstructingPreferredSizeWidget? navigationBar;