simple flutter demo

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          backgroundColor: Colors.red,
          title: Text("Demo"),
        ),
        body: Center(
          child: Text("Hello world app"),
        ),
        floatingActionButton: FloatingActionButton(
          backgroundColor: Colors.red,
          child: Icon(Icons.add),
        ),
      ),
    );
  }
}