MC-4014: PageBuilder Performance Is Bad With Minimal Content

- Fix offscreen sections within slider TinyMCE

Author: davemacaulay

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

@@ -44,6 +44,10 @@
         .inline-wysiwyg {
             line-height: 1.3;
             min-height: 50px;
+
+            .mce-offscreen-selection {
+                left: -99999px;
+            }
         }
         .mce-tinymce-inline {
             left: -2px !important;