first implementation finished

app/lib/utils/ui_helper.dart

@@ -0,0 +1,14 @@
+import 'package:flutter/material.dart';
+
+void showErrorMessage(BuildContext context, String message) {
+  final snackBar = SnackBar(
+    content: Text(
+      message,
+      style: TextStyle(
+        color: Theme.of(context).colorScheme.error,
+      ),
+    ),
+    backgroundColor: Theme.of(context).colorScheme.onError,
+  );
+  ScaffoldMessenger.of(context).showSnackBar(snackBar);
+}