Add persistent storage

lib/service/theme_bloc.dart

@@ -1,5 +1,6 @@
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter/services.dart';
+import 'package:get_it/get_it.dart';
 import 'package:meta/meta.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
@@ -12,14 +13,13 @@ class SetTheme {
 }
 
 class ThemeBloc extends Bloc<SetTheme, Brightness> {
-  final SharedPreferences prefs;
-
   ThemeBloc({
-    required this.prefs,
     required Brightness init,
   }) : super(init) {
     on<SetTheme>((event, emit) {
-      prefs.setBool('darkTheme', event.isDark);
+      GetIt.instance
+          .get<SharedPreferences>()
+          .setBool('darkTheme', event.isDark);
       emit(event.isDark ? Brightness.dark : Brightness.light);
     });
   }