Flutter example of theming a app

template.dart

import 'package:flutter/material.dart';

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: Colors.brown,
        appBarTheme: const AppBarTheme(
          color: Colors.green,
        ),
      ),
      debugShowCheckedModeBanner: false,
      home: MyWidget(),
    );
  }
}

class MyWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
          title: Text('Teste App', style: Theme.of(context).textTheme.headlineMedium,),
        ),
      body: Column(
        children: [
        Text('Hello, World!',
          style: Theme.of(context).textTheme.titleMedium),
        Text('Hello, World!',
          style: Theme.of(context).textTheme.headlineMedium),
        Text('Hello, World!',
          style: Theme.of(context).textTheme.headlineMedium),
          
        ],
      ),
    );
  }
}