Is "horizontal reading" worse than reading two files?
What if the other file is actually 30 files compiled with SASS?
What if they're 30 files, compiled with SASS, and written by a bunch of devs who don't know CSS well, didn't use BEM or anything to name things well, and didn't organise them at all?
Tailwind isn't better than great CSS, but it's significantly better than bad CSS.