Flutter: 矩形边框

      Center(
        child: Material(
          shape: const BeveledRectangleBorder(
            borderRadius: BorderRadius.all(Radius.circular(40)),
            side: BorderSide(color: Colors.black,  2),
          ),
          color: Colors.yellow,
          child: Container(
            height: 200,
             200,
          ),
        ),
      ),