MAGETWO-37596: Stabilize story after testing

Author: slopok

app/code/Magento/Ui/view/base/web/js/modal/modal.js

@@ -34,7 +34,7 @@ define([
             modalAction: '[data-role="action"]',
             appendTo: 'body',
             wrapperClass: 'modals-wrapper',
-            overlayClass: 'overlay_magento',
+            overlayClass: 'modals-overlay',
             responsiveClass: 'modal-slide',
             modalLeftMargin: 45,
             closeText: $.mage.__('Close'),

app/design/adminhtml/Magento/backend/web/css/source/components/_popups.less

@@ -514,7 +514,7 @@
 
 .overlay_magento {
     &:extend(.ui-widget-overlay all);
-    z-index: 900;
+    z-index: 800 !important;
 }
 
 //

lib/web/css/source/components/_modals.less

@@ -106,6 +106,13 @@
     width: 100vw;
 }
 
+// Modals overlay
+
+.modals-overlay {
+    &:extend(.ui-widget-overlay all);
+    z-index: @overlay__z-index;
+}
+
 .modal-slide,
 .modal-popup {
     .abs-modal();