The blog post: https://decodingvibes.com/blog/genz-and-frutiger-aero/
(There were also a few INI-style config files, mainly to define colors of dynamic things like text. For most skins you would just need to copy the defaults and maybe change a few color hex codes.)
Artists did some wild stuff with it. A few fun examples:
https://macthemes.garden/themes/c7005c70d044-Wrecked-Angles/
https://macthemes.garden/themes/2852d54a73a3-Windows-98/
https://macthemes.garden/themes/0219829f8a23-HolySmoke/
https://macthemes.garden/themes/8405ec7f05e4-MacPlaza/
https://macthemes.garden/themes/92b39d18db52-MammaMia/
red-iron-pine•2h ago
Lalabadie•1h ago
Archived soundbite: https://archive.org/details/youtube-LWKxtWEkS1c