"Significantly worse"? Just getting away from a serif font makes the third you linked way better to me. The text contrast is still good (to head off the "but it's not pure black on white!" cargo cult) and colored headers are distinctive but not obnoxious.
> Just getting away from a serif font makes the third you linked way better to me.
The original one doesn't use CSS at all (and doesn't set fonts with serifs), while all the others try to alter fonts and/or their sizes, potentially changing them from ones set/preferred by a user to ones set by a webmaster. thebestmotherfucking.website also tries to override colors. I think these are good (simple, hence easy to reason about) examples of the awkwardness that comes out of styling (and complexity of relatively simple decisions): some would assume certain user agents and settings, and possibly that users don't configure those. Not to mention that some may actually prefer serifs and other common defaults.
Would be amusing if that progression of websites grew even further, to heavy and heavily styled SPAs, completely reversing the original message.
Oh no, they used CSS! Heaven forfend one delicately and with restraint use something supported in nine thousand, nine hundred and ninety-nine out of ten thousand browsers. Heaven forfend. A pox on their house.
"Sets fonts" is misleading--the creator knows and must know that the default in virtually every browser is whatever dog's-breakfast default serif there is. (Yes, yes, "the browser can change it," because we all know that every user is an artisanal crafter of browser preferences and truly, deeply cares to do that instead of go to a site where somebody thought that through in its presentation.)
It's not 1997 anymore. HTML is no longer a document markup language, it is an application-and-presentation toolkit, and whether or not you or I like it--I don't particularly, there are better ones--doesn't excuse doing bad work because we pretend users who happen to be fully congruent with ourselves want it.