18-snack-bar-05-duration.dart

 Widget _snackDuration() => SnackBar(
        content: Text(
          "You have a message!",
          style: TextStyle(
            color: TEXT_BLACK,
            fontSize: 20,
          ),
          textAlign: TextAlign.center,
        ),
        backgroundColor: BLUE_LIGHT,
        duration: Duration(milliseconds: 100),
      );