Automatically switch theme based on system theme

lib/main.dart

@@ -25,10 +25,9 @@ class MyApp extends StatelessWidget {
 
     return MaterialApp(
       title: 'Gym App',
-      theme: ThemeData(
-        primarySwatch: Colors.blue,
-        visualDensity: VisualDensity.adaptivePlatformDensity,
-      ),
+      themeMode: ThemeMode.system,
+      darkTheme: ThemeData.dark(),
+      theme: ThemeData.light(),
       initialRoute: '/home',
       routes: routes,
       navigatorKey: navigatorKey,