Widget Stack

main.dart

import 'package:flutter/material.dart';

void main() => runApp(App());

class App extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Demo'),
      ),
      body: Stack(
        children: <Widget>[
          Container(
            width: 200.0,
            height: 200.0,
            color: Colors.red,
          ),
          Container(
            width: 180.0,
            height: 180.0,
            color: Colors.green,
          ),
          Container(
            width: 160.0,
            height: 160.0,
            color: Colors.orange,
          ),
          Align(
            alignment: Alignment.center,
            child: Text('Center'),
          ),
          Positioned(
            right: 24.0,
            child: Text('Right 24'),
          ),
        ],
      ),
    );
  }
}