Tailwind has a page in their documentation about optimizing for production (https://tailwindcss.com/docs/optimizing-for-production), it has steps for the Tailwind CLI and PostCSS. In case you are using a framework, it says to check the framework documentation to see what you should do / if it is done automatically for you.
This might be done automatically in Astro, however I couldn't find anything about it in the docs. Should I do anything or is this being done at build?