如何更改OutlinedButton的边框颜色

import 'package:flutter/material.dart';

final customTheme = ThemeData(
  // 设置主题颜色
  primarySwatch: Colors.blue,
  // 设置OutlinedButton的边框颜色
  outlinedButtonTheme: OutlinedButtonThemeData(
    style: ButtonStyle(
      side: MaterialStateProperty.all<BorderSide>(
        BorderSide(color: Colors.red), // 设置边框颜色为红色
      ),
    ),
  ),
);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: customTheme, // 使用自定义主题
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('OutlinedButton示例'),
      ),
      body: Center(
        child: OutlinedButton(
          onPressed: () {},
          child: Text('OutlinedButton'),
        ),
      ),
    );
  }
}