I interviewed Diana Mounter who leads their design systems team about this a while back: http://www.fullstackradio.com/75
Airbnb (332kb, 54 text colors, 72 background colors, 48 font sizes): https://cssstats.com/stats?url=http%3A%2F%2Fairbnb.com&ua=Br...
Walmart (178kb, 32 text colors, 22 background colors, 64 font sizes): https://cssstats.com/stats?url=http%3A%2F%2Fwalmart.com&ua=B...
Twitter (630kb, 36 text colors, 50 background colors, 46 font sizes): https://cssstats.com/stats?url=http%3A%2F%2Ftwitter.com&name...
GitHub (658kb, 157 text colors, 141 background colors, 55 font sizes): https://cssstats.com/stats?url=http%3A%2F%2Fgithub.com&name=...
These are not stylesheets I want to emulate. As I mentioned in my other reply, GitHub is actively moving towards a more utility-based approach to solve this problem.
Compare this to a fairly large app where the CSS and markup were completely rewritten using Tailwind by a friend of mine recently:
https://cssstats.com/stats?link=https%3A%2F%2Fapp.churchsoci...
41kb (8.1kb gzipped), 15 text colors, 44 background colors, 22 font sizes. Pretty good, no?
This is all the CSS needed to render almost the entire app from mobile to desktop widths, in both light and night themes. The "utility CSS" is generated by a framework and not something engineers have to be concerned with when writing components.
Check your facts ;)
Functional CSS makes for an unscaleable, inconsistent, unmaintainable dumpster fire of styles that is objectively worse than just writing regular CSS.
<sarcasm> But it's convenient, right? So who cares! AirBnB, Facebook, Walmart, Github, and Twitter are all probably wrong anyway. </sarcasm>