MC-3392: Hide Content block/ container from the stage

- Fix static failure

Author: davemacaulay

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/form/element/uploader/preview/_image.less

@@ -197,4 +197,4 @@
     &.dragging .file-uploader {
         visibility: visible;
     }
-}
+}