PB-265: Video background for Banner

- fix slider uploader

Author: omiroshnichenko

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/slide/_default.less

@@ -179,6 +179,15 @@
             max-width: 100%;
             word-break: break-word;
         }
+
+        .dragging {
+            height: 100%;
+            left: 0;
+            position: absolute;
+            top:0;
+            width: 100%;
+            z-index: 4;
+        }
     }
 
     & + [data-content-type='slide'] {