appbar-and-bottombar.dart

return Scaffold(
      appBar: PreferredSize(
          child: Container(color: Colors.red),
          preferredSize: Size.fromHeight(50.0)),
      bottomNavigationBar: Container(height: 50.0, color: Colors.red),
      floatingActionButton: Container(
        width: 50.0,
        height: 50.0,
        child: Center(
          child: FittedBox(
            child: FloatingActionButton(
              onPressed: () {},
              child: Icon(Icons.arrow_upward),
            ),
          ),
        ),
      ),
      body: ListView(
        children: List.generate(
            200,
            (index) => ListTile(
                  title: Text(index.toString()),
                )),
      ),
    );