поправки

lib/main.dart

@@ -30,19 +30,13 @@ class MyHomePage extends StatefulWidget {
 }
 
 class _MyHomePageState extends State<MyHomePage> {
-  int _counter = 0;
-
-  void _incrementCounter() {
-    setState(() {
-      _counter++;
-    });
-  }
+  final Color _color = Colors.pink.shade300;
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(
-        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
+        backgroundColor: _color,
         title: Text(widget.title),
       ),
       body: const MyWidget(),