Entry Point… runApp()

void main() {
  runApp(const MainWidget());
}

The MainWidget

build() - returns a widget, this is the method that will be run to build your widget. This goes with all other widgets not just the initial one.

class MainWidget extends StatelessWidget {
  const MainWidget({super.key});

  @override
  Widget build(BuildContext context) {
    final ThemeData themeData = ThemeData();
    const String appName = 'Recipe Calculator';

    return MaterialApp(
      title: appName,
      theme: themeData.copyWith(
        colorScheme: themeData.colorScheme.copyWith(
          primary: Colors.grey,
          secondary: Colors.black,
        ),
      ),
      home: const MyHomePage(title: appName),
    );
  }
}