https://www.theregister.co.uk/2018/07/09/nostalgic_for_that_windows_9x_look/

How many baby boomers does it take to set up GitHub? Just one – but you've got to make it look like a 1990s Windows build.

That seems to be the reasoning behind "GitHub Windows Edition", billed as “a user style which transforms GitHub's pages into [a] GUI resembling Windows 9x” in a browser window.