CallPage.dart

@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Agora Group Calling'),
      ),
      backgroundColor: Colors.black,
      body: Center(
        child: Stack(
          children: <Widget>[
            _viewRows(),
            _panel(),
            _toolbar(),
          ],
        ),
      ),
    );
  }