Resolve "Improve topbar buttons"

Closes #18 (closed)

lib/nav/application_navigation_definition.dart

@@ -77,10 +77,10 @@ class AppBarButton {
   });
 
   Widget render(BuildContext context) {
-    return ElevatedButton(
+    return TextButton(
       onPressed: () => onPressed!(context),
       onLongPress: () => onLongPress!(context),
-      style: ElevatedButton.styleFrom(
+      style: TextButton.styleFrom(
         shape: const CircleBorder(),
         iconColor: Theme.of(context).colorScheme.onSurface,
       ),