Flutter App:背景不会从黑色变为青色

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Container(
          color: Colors.cyan, // 设置背景颜色为青色
          child: Center(
            child: Text(
              'Hello Flutter',
              style: TextStyle(
                fontSize: 24,
                color: Colors.white,
              ),
            ),
          ),
        ),
      ),
    );
  }
}