Unsure if you're trolling: your attitude is basically big cashed up corporates squatting on their users' devices, because their devs are too lazy, unempathetic, incompetent, or all three, to pick a better solution.
This shit is why basic webpages drain my battery and burn my lap.
No, the attitude is that CSS is for decoration to meet the User’s needs (colors, dark or light mode, font sizes and adjustments for accessibility, etc). So moving it to backend is a bad idea because you remove the users ability to customize or at worst make your entire service delayed both for all users and for the user who needs the customization by doing it on the server. (now I understand the tool featured here is for precompile, but this is the argument i was making before I knew that).
The whole industry of React and similar giant frameworks is to offload functionality to the browser and make the server only a data source - you reduce the amount of data that has to go through tight pipes and speed up the responsiveness of the site for your users. Basic pages drain your battery for sure. There is a gradient of that and putting CSS in the front end is the wise minimal end of that gradient, while React is the opposite side of it, then add SQLite and you go even more client heavy. It depends on the tool you are building - some justify it, but many don’t.
This shit is why basic webpages drain my battery and burn my lap.