The stylesheet that was 2,100 lines and stayed

A hand-written design system, evaluated against a framework, and kept for a reason that is not technical.

the honest accounting:

  2,100 lines, of which
    412  layout primitives — grid, stack, cluster
    880  components
    290  tokens, generated
    518  utilities, which is where a framework wins

  people who can change it confidently: 1
  people who could change a framework's classes
    confidently on day one: everybody

and it stayed, because the 518 lines are the part a
framework replaces and the other 1,582 are not.

The utility layer is genuinely better in a framework and it is a quarter of the file, which is the arithmetic that decides this. Replacing a quarter of a stylesheet with a dependency, a build step and a class vocabulary is a trade worth making on a new project and a poor one on an existing system where the other three quarters would have to interoperate with it.