Dart pad example of approximate device layout

main.dart

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        scaffoldBackgroundColor: Colors.blueAccent[100],
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: [
            const Spacer(),
            Expanded(
              child: Stack(
                children: [
                  Container(
                    color: Colors.orange,
                    padding: const EdgeInsets.symmetric(
                      horizontal: 10,
                    ),
                    child: Stack(
                      children: [
                        Container(
                          height: 1771,
                          width: 873,
                          color: Colors.black,
                          child: const Center(
                            child: Text(
                              'Hello world!',
                              style: TextStyle(color: Colors.white),
                            ),
                          ),
                        ),
                        Container(
                          margin: const EdgeInsets.only(
                            top: 135,
                            right: 100,
                          ),
                          width: 15,
                          height: 45,
                          color: Colors.blue,
                        ),
                      ],
                    ),
                  ),
                  Container(
                    margin: const EdgeInsets.only(
                      top: 135,
                      right: 100,
                    ),
                    width: 15,
                    height: 45,
                    color: Colors.green,
                  ),
                ],
              ),
            ),
            const Spacer(),
          ],
        ),
      ),
    );
  }
}