Themes in 3 lines

main2.dart

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    //STEP 2 - replace MaterialApp with GetMaterialApp
    return GetMaterialApp(
      title: 'Theme change using Get',
      theme: ThemeData.light().copyWith(primaryColor: Colors.green),
      darkTheme: ThemeData.dark().copyWith(primaryColor: Colors.purple),
      // NOTE: Optional - use themeMode to specify the startup theme
      themeMode: ThemeMode.system,
      home: MyHomePage(),
    );
  }
}