【Flutter】Material 3 での基本的な色設定

import 'package:flutter/material.dart';
void main() {
  runApp(const MyApp());
}
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
          useMaterial3: true,
          colorScheme: ColorScheme.fromSwatch(
            brightness: Brightness.light,
            primarySwatch: Colors.purple,
            accentColor: Colors.red,
          ),
          scaffoldBackgroundColor: Colors.blue),
      darkTheme: ThemeData(
          useMaterial3: true,
          colorScheme: ColorScheme.fromSwatch(
            brightness: Brightness.dark,
            primarySwatch: Colors.purple,
            accentColor: Colors.red,
          ),
          scaffoldBackgroundColor: Colors.blue),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}
class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4!.copyWith(
                    color: Theme.of(context).colorScheme.secondary,
                  ),
            ),
            OutlinedButton(onPressed: () {}, child: Text('OutlinedButton')),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}