Maps Sample V2 - add widget on top of map

main.dart

body: Stack(
  children: <Widget>[
    GoogleMap(
      onMapCreated: _onMapCreated,
      initialCameraPosition: CameraPosition(
        target: _center,
        zoom: 11.0,
      ),
    ),
    Padding(
      padding: const EdgeInsets.all(16.0),
      child: Align(
        alignment: Alignment.topRight,
        child: FloatingActionButton(
          onPressed: () => print('button pressed'),
          materialTapTargetSize: MaterialTapTargetSize.padded,
          backgroundColor: Colors.green,
          child: const Icon(Icons.map, size: 36.0),
        ),
      ),
    ),
  ],
),