如何在flutter桌面应用程序(macOS)中添加半透明效果？

dependencies:
  flutter:
    sdk: flutter
  flutter_macos: ^0.3.0

import 'package:flutter/material.dart';
import 'package:flutter_macos/flutter_macos.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return WidgetsApp(
      builder: (context, _) {
        return MacosWindow(
          title: 'My App',
          child: MyHomePage(),
        );
      },
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      // 添加半透明效果
      color: Colors.black.withOpacity(0.5),
      child: Center(
        child: Text(
          'Hello, World!',
          style: TextStyle(fontSize: 24),
        ),
      ),
    );
  }
}