Overlaz del botón de contorno de Flutter

// OutlineButton is deprecated. Use OutlinedButton in place (notice the -d)
OutlinedButton(
   style: ButtonStyle(
       overlayColor: MaterialStateProperty.resolveWith(
            (state) => Colors.red)),
   child: Text('Fermer'),
   onPressed: () {
       Navigator.of(context).pop();
   },
Joyful Code