Merge remote-tracking branch 'origin/MC-15073' into 2.2.8-develop-pr82

Author: zakdma

app/design/adminhtml/Magento/backend/Magento_Backend/web/css/source/module/_menu.less

@@ -271,17 +271,9 @@
 
         &._show {
             > .submenu {
-                display: block;
-                float: left;
-                left: 100%;
-                max-width: 1640px;
-                min-height: 98.65%;
-                min-width: 100%;
-                overflow-x: scroll;
-                position: absolute;
                 transform: translateX(0);
                 visibility: visible;
-                z-index: 698;
+                z-index: @submenu__z-index;
             }
         }
     }