Normally if you place three the same size icons in a stack, they will stands on top of each other, then we can use 'Align' and 'Position' to positioning them:

class MyApp extends StatelessWidget { @override Widget build(BuildContext context) {   return MaterialApp(     home: Scaffold(       body: SizedBox.expand(         child: Stack(           children: 
     
      [             Icon(               Icons.camera,               size: 100,               color: Colors.red,             ),             Align(                 alignment: Alignment.center,                 child: Icon(                   Icons.camera,                   size: 100,                   color: Colors.blue,                 )),             Positioned(                 bottom: 20,                 child: Icon(                   Icons.camera,                   size: 100,                   color: Colors.green,                 ))           ],         ),       ),     ),   ); }}