Comment by matthberg

I just discovered that feature due to your mistake, so thank you!

For similarly newly enlightened people it's a feature of MediaWiki (which Wikipedia runs on) and there are five (plus two) themes selectable with ?useskin= values:

- timeless (as seen above): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=timeles...

- monobook (default 2004-2009): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=monoboo...

- vector (default 2010-2021): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=vector

- vector-2022 (desktop default 2022-): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=vector-...

- minerva (mobile default): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=minerva

- modern (delightedly dated, deprecated): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=modern

- cologneblue (also ancient and anti-favored): https://en.wikipedia.org/wiki/Wikipedia:Skin?useskin=cologne...