new Material(
      elevation: 2.0,
      child: new Opacity(
        opacity: 0.3,
        child: new Container(
          padding: new EdgeInsets.all(20.0),
          child: new Image.asset("assets/<your icon>", fit: BoxFit.cover, color: Colors.grey),
          decoration: new BoxDecoration(
            border: new Border.all(
              width: 2.0, color: const Color(0x40000000)),
              borderRadius: const BorderRadius.all(const Radius.circular(5.0)
            )
          )
        )
      )
  );