main_stateless_widget.dart

import 'package:flutter/material.dart';

void main() => runApp(
      MaterialApp(
        title: "My CodeJourney Flutter app",
        home: Scaffold(
          appBar: AppBar(
            title: Text("My First App"),
          ),
          body: MyFirstWidget(),
        ),
      ),
    );

class MyFirstWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(8.0),
      child: Text(
        "Hello MyFirstWidget!",
        style: TextStyle(color: Colors.green),
      ),
    );
  }
}