On Special:Undelete, there are two buttons for preview and diff. These buttons do not have any space between them and the whole page does not use OOUI, like all other UI parts on this special page.
- The funtionality of the page has not changed
- The "View difference" page of Special:Undelete is converted to use OOUI.
The code for this special page is at https://phabricator.wikimedia.org/source/mediawiki/browse/master/includes/specials/SpecialUndelete.php and the buttons are defined in showRevision on lines 473 to 486.