Example of using Stack in Flutter

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(primarySwatch: Colors.green),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Flutter Demo Home Page')),
      body: Center(
        child: Stack(
          alignment: AlignmentDirectional.topCenter,
          clipBehavior: Clip.none,
          children: [
            Card(
              color: Colors.green.shade50,
              child: const Padding(
                padding: EdgeInsets.fromLTRB(32, 56, 32, 32),
                child: Text('Successful', style: TextStyle(fontSize: 32)),
              ),
            ),
            Positioned(
              top: -40,
              child: Container(
                child: const Icon(Icons.gpp_good, color: Colors.green, size: 48),
                padding: const EdgeInsets.all(16),
                decoration: BoxDecoration(
                  color: Colors.white,
                  border: Border.all(color: Colors.green.shade50, width: 4),
                  shape: BoxShape.circle,
                ),
              ),
            )
          ],
        ),
      ),
    );
  }
}