show modal barrier when displaying sheet

app/lib/features/search_browser/presentation/screens/browser.dart

@@ -334,10 +334,13 @@ class KagiScreen extends HookConsumerWidget {
                     return true;
                   }
                 },
-                child: SafeArea(
+                child: Stack(
+                  children: [
+                    SafeArea(
                       child: AnimatedIndexedStack(
                         duration: const Duration(milliseconds: 250),
-                    transitionBuilder: (child, animation, secondaryAnimation) =>
+                        transitionBuilder:
+                            (child, animation, secondaryAnimation) =>
                                 SharedAxisTransition(
                           animation: animation,
                           secondaryAnimation: secondaryAnimation,
@@ -360,6 +363,13 @@ class KagiScreen extends HookConsumerWidget {
                         children: [const LandingContent(), ...webViews.values],
                       ),
                     ),
+                    if (displayedSheet != null)
+                      ModalBarrier(
+                        color: Theme.of(context).dialogTheme.barrierColor ??
+                            Colors.black54,
+                      ),
+                  ],
+                ),
               );
             },
           ),