Ширина закусочной трепетана

ScaffoldMessenger.of(context).showSnackBar(
          SnackBar(
          behavior: SnackBarBehavior.floating, // default SnackBarBehavior.fixed.
          width: 250.0, // It can not be used if margin is specified.
          content: const Text('Awesome!'),
          ),
    );
Sore Serval