如何在Flutter中进行主题和样式的管理？

final ThemeData myTheme = ThemeData(
  brightness: Brightness.light,
  primaryColor: Colors.blue,
  accentColor: Colors.green,
  fontFamily: 'Roboto',
);

MaterialApp(
  title: 'My App',
  theme: myTheme,
  home: MyHomePage(),
);

Text(
  'Hello, World!',
  style: Theme.of(context).textTheme.headline1,
);

ThemeData newTheme = Theme.of(context).copyWith(
  primaryColor: Colors.red,
);

Theme(
  data: Theme.of(context).copyWith(
    accentColor: Colors.pink,
  ),
  child: MyWidget(),
);