last time this came up people appreciated my collection

https://alexbsoft.github.io/win95.css/ windows 95

https://bootstra386.com/ 1980's websites

https://botoxparty.github.io/XP.css/ windows xp

https://code.divshot.com/geo-bootstrap/ geocities

https://cs16.samke.me/ counter strike 1.6

https://edwardtufte.github.io/tufte-css/ edward tufte

https://jdan.github.io/98.css/ windows 98

https://khang-nd.github.io/7.css/ windows 7

https://micah5.github.io/PSone.css/ playstation one

https://nostalgic-css.github.io/NES.css/ nes

https://sakofchit.github.io/system.css/ apple system

https://snes-css.sadlative.com/ snes

https://thesimscss.inbn.dev/ the sims

and don't forget Windows 93! https://www.windows93.net

Another one to add to your list, which is another collection of vintage styles

https://nielssp.github.io/classic-stylesheets/

Geocities is broken otherwise thanks!