Master Pages Updated
On 10.1.0 application, the tooltip of close button on Quick Selector pages and add record pop-up pages come from resource files. In addition, the style of email master page is changes. As a result, Email and Popup master pages are updated during migration.
Migration effects
During migration, the Email and Popup master pages are replaced with updated versions.
What you should do
After migration, re-apply any customizations you may have made to the original files.