how to make a widget fit to its parent widget in flutter code example

Example: flutter set widget width to 50% o parent

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("MediaQuery"),
      ),
      body: Container(
        width: MediaQuery.of(context).size.width * 0.5,
        height: MediaQuery.of(context).size.height * 0.5,
      ),
    );
  }