fix https://redmine.weseek.co.jp/issues/86678 again

packages/app/src/styles/_sidebar.scss

@@ -79,8 +79,7 @@
         }
       }
 
-      .grw-sidebar-content-container {
-        position: relative;
+      .simplebar-mask {
         z-index: 110; // greater than the value of .grw-navigation-draggable to fix https://redmine.weseek.co.jp/issues/86678
       }
     }