Custom Style for SettingsScreen

[ThraaxSession]

Hi!
Currently it's only possible to set a background color for the Appbar. If I want to add gradient, it's not possible.

Current:

//Would be awesome to have option to add custom style like this:
...
flexibleSpace: BoxDecoration(
        gradient: LinearGradient(
            begin: Alignment.centerLeft,
            end: Alignment.centerRight,
            colors: <Color>[
              Colors.blue,
              Colors.deepPurple,
              Colors.white
            ]
        )
    )