changing tailwind scss files.

I want to replace the baked in styles for form inputs with this: https://notiz.dev/blog/floating-form-field-with-tailwindcss.
I've tried commenting out the input in _forms.scss, creating a _new_forms.scss and pointing to that file instead in application.scss. Neither works: I still get the old CSS. 

What am I doing wrong? (or put another way, how do I force recompiling into application.css?)