Why do I got 'Invalid constant value.' while trying to apply the theme that separated to another dart file? [Dart, Flutter]

When I'm trying to load theme data from another dart file, 'Invalid constant value.' is occured.

I apologize for my limited proficiency in English and for using ChatGPT to upload my question.
And ChatGPT did not help in this issue.

I am attempting to separate the theme into a separate file for refactoring and reusability of the source code. However, as mentioned in the title, I am encountering an error. Is there any way to resolve this issue?

Here are main.dart and selfmade_basic_interface.dart files.

main.dart

import 'package:flutter.material.dart';
import './interface/000_selfmade_basic_interface.dart';

void main() => runApp(const MainApp());

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      theme: selfmadeTheme, // <- Here is where an error occured.
      home: Scaffold(
        body: SizedBox(),
      ),
    );
  }
}

selfmade_basic_interface.dart

import 'package:flutter/material.dart';

ThemeData selfmadeTheme = ThemeData(
  primarySwatch: const MaterialColor(
    0xff424242,
    {
      50: Color(0xfffafafa),
      100: Color(0xfff5f5f5),
      200: Color(0xffeeeeee),
      300: Color(0xffe0e0e0),
      350: Color(0xffd6d6d6),
      400: Color(0xffbdbdbd),
      500: Color(0xff9e9e9e),
      600: Color(0xff757575),
      700: Color(0xff616161),
      800: Color(0xff424242),
      850: Color(0xff303030),
      900: Color(0xff212121)
    },
  ),
  scaffoldBackgroundColor: const Color(0xff303030),
  drawerTheme: const DrawerThemeData(
    backgroundColor: Color(0xff424242),
  ),
  listTileTheme: const ListTileThemeData(
    textColor: Colors.white,
    iconColor: Colors.white,
  ),
  textTheme: const TextTheme(
    bodySmall: TextStyle(
      color: Colors.white,
    ),
    bodyMedium: TextStyle(
      color: Colors.white,
    ),
  ),
  scrollbarTheme: ScrollbarThemeData(
    thumbColor: MaterialStateProperty.all(Colors.grey),
    thumbVisibility: MaterialStateProperty.all<bool>(true),
  ),
);

The issue was the const keyword. As you made the MaterialApp widget a constant using the const keyword, it expects the theme also a constant. But it is not constant. So removing const keyword before the MaterialApp will resolve your issue.