Broken out from T173800.
The MinervaNeue skin has been enabled on all wikis and is available from Special:Preferences. It doesn't work too well with Wikisource,org
This skin is listed in the Preferences / Appearance of en.Wikisource (desktop), although on the Special Pages it is listed for mobile. But, it is altogether missing from the mobile Wikisource Settings.
There is no over / under editing mode, and in the side by side editing, the original page (djvu) is so small that it is illegible, as well as the window it is displayed in, is so narrow that the page is cut off.
PurgeTab Gadget incompatibility
On the desktop, after switching to the MinervaNeue skin, the hamburger menu is not working. It just opens a blank page on the left which takes up half of the screen. < bug with local gadget) [Tracked in https://wikisource.org/wiki/MediaWiki_talk:Gadget-purgetab.js]