edit design

lib/app.dart

@@ -68,7 +68,7 @@ class _AppState extends State<App> {
       navBarStyle: NavBarStyle.style6,
       backgroundColor: Theme.of(context).colorScheme.surface,
       decoration: const NavBarDecoration(
-        border: Border.symmetric(vertical: BorderSide.none, horizontal: BorderSide(color: Colors.grey, width: 1))
+        border: Border(top: BorderSide(width: 1, color: Colors.grey)),
       ),
       screenTransitionAnimation: const ScreenTransitionAnimation(animateTabTransition: true, curve: Curves.ease, duration: Duration(milliseconds: 200)),
       screens: const [