For those who weren't aware, Jack Phoenix and I have drafted a Request for Comment[1] and related initial patch[2] proposing to merge the logic from the Theme extension[3] into MediaWiki core.

From the RfC: This will provide built-in functionality that skins can implement in a simple and consistent manner, enabling user- or site-selection of css variations of a given skin, such as a dark version or a layout with more colours.

The RfC itself covers in detail the distinction between skins and themes as well as several use cases and issues surrounding the current situation, but the key point here is thus: with this functionality, we will be able to not just more easily implement night[4], winter, and accessibility[5] modes in skins such as Vector and Timeless, but also much more consistently, and in a manner that can then be developed to better and more consistently use the variables defined by the skins even outside of the themes themselves.

Currently, the Theme functionality is limited to the extension itself and a few skins that replicate key parts with varying amounts of fidelity, which not only results in a bit of a mess in terms of code fragmentation, but also limits what we can do with the skins themselves due to the added dependency. We would like to fix this, and thus invite everyone interested to review our proposal and please, comment if you have concerns or see any issues.

-I

See: [1] https://www.mediawiki.org/wiki/Requests_for_comment/Themes_in_core [2] https://gerrit.wikimedia.org/r/#/c/465451/ [3] https://www.mediawiki.org/wiki/Extension:Theme [4] https://meta.wikimedia.org/wiki/Community_Wishlist_Survey_2019/Reading/Night... [5] https://meta.wikimedia.org/wiki/Community_Wishlist_Survey_2019/Reading/Acces...