theme.dart

import 'package:flutter/material.dart';
import 'package:get/get.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Material App',
      themeMode: ThemeMode.system,
      darkTheme: ThemeData.dark(),
      theme: ThemeData.light(),
      home: Home(),
    );
  }
}

class Home extends StatelessWidget {
  const Home({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: ThemeClass.of(context).color,
    );
  }
}

class ThemeClass {
  final Color _darkColor = Colors.blue;
  final Color _lightColor = Colors.green;
  Color? color;
  ThemeClass.of(BuildContext context) {
    print(context.mediaQuery.platformBrightness);
    if (MediaQuery.of(context).platformBrightness == Brightness.dark) {
      color = _darkColor;
    } else {
      color = _lightColor;
    }
  }
}