How do I fix "Cannot apply unknown utility class" with Svelte and Tailwind?

I'm working on a Svelte app that uses Tailwind. I recently upgraded from Tailwind 3 to 4, and was getting this error: Cannot apply unknown utility class text-blue-200. Are you using CSS modules or similar and missing @reference? https://tailwindcss.com/docs/functions-and-directives#reference-directive It took a while to find the source, but the app had a Svelte, whose CSS imported a CSS File, like…