如何在Appbar flutter上重叠项目

import 'package:flutter/material.dart';

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Appbar重叠项目',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Appbar重叠项目'),
        ),
        body: Stack(
          children: <Widget>[
            // 重叠的项目
            Positioned(
              top: 0,
              left: 0,
              right: 0,
              child: Container(
                height: 200,
                color: Colors.blue,
              ),
            ),
            // 其他内容
            Positioned(
              top: 100,
              left: 16,
              child: Text(
                '重叠的项目',
                style: TextStyle(fontSize: 20, color: Colors.white),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

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