17-simple-dialog-06-shape.dart

 Widget _shapeDialog() => SimpleDialog(
        title: Text(
          "Be careful!",
          textAlign: TextAlign.center,
        ),
        children: <Widget>[
          Text(
            "If you write a message, you should care about the message.",
            textAlign: TextAlign.center,
          ),
        ],
        backgroundColor: BLUE_LIGHT,
        elevation: 4,
        shape: StadiumBorder(
          side: BorderSide(
            style: BorderStyle.none,
          ),
        ),
      );