如何在flutter应用栏中添加圆角？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          shape: ContinuousRectangleBorder(
            borderRadius: BorderRadius.vertical(
              bottom: Radius.circular(20.0),
            ),
          ),
          title: Text('圆角应用栏'),
        ),
        body: Center(
          child: Text('这是一个圆角应用栏示例'),
        ),
      ),
    );
  }
}