### Deprecated: preprocessors support
> ##### Sass, Less, and Stylus > Tailwind CSS v4.0 is a full-featured CSS build tool designed for a specific workflow, and is not designed to be used with CSS preprocessors like Sass, Less, or Stylus. > > Think of Tailwind CSS itself as your preprocessor — you shouldn't use Tailwind with Sass for the same reason you wouldn't use Sass with Stylus. > > Since Tailwind is designed for modern browsers, you actually don't need a preprocessor for things like nesting or variables, and Tailwind itself will do things like bundle your imports and add vendor prefixes.
* [Compatibility](https://tailwindcss.com/docs/compatibility#sass-less-and-stylus) - TailwindCSS v4 Docs
> Sorry for the inconvenience here, however **right now we don't support migrating `.scss` or `.less` files**. Doing so would require us to be able to understand the scss/sass and less syntax to make changes. But even if we do that, Tailwind CSS v4 isn't really compatible with these files anyway. > > I would recommend to see if you can rename the file(s) to `.css` and try again. You might notice that sometimes people use scss for features such as nested css, which should just work already in Tailwind CSS v4 (and modern browsers). So there is a good chance that you might not need `.scss` files at all. > > Again, sorry about the inconvenience here, but if you can migrate to normal `.css` files, then upgrading using the upgrade tool should just work.
* [`tailwindlabs/tailwindcss` #15716 by RobinMalfait:<br>Migration tool doesn't recognize .scss files](https://github.com/tailwindlabs/tailwindcss/issues/15716#issuecomment-2619593290) - GitHub
Simply put, TailwindCSS v4 removes the need for Sass and other preprocessors. The TailwindCSS v4 ecosystem can independently provide the functionality that these preprocessors offered.

Although it's not explicitly stated in the question, after reading the comments, I thought it would be better to highlight an important change here as well.
### Deprecated: preprocessors support
> ##### Sass, Less, and Stylus > Tailwind CSS v4.0 is a full-featured CSS build tool designed for a specific workflow, and is not designed to be used with CSS preprocessors like Sass, Less, or Stylus. > > Think of Tailwind CSS itself as your preprocessor — you shouldn't use Tailwind with Sass for the same reason you wouldn't use Sass with Stylus. > > Since Tailwind is designed for modern browsers, you actually don't need a preprocessor for things like nesting or variables, and Tailwind itself will do things like bundle your imports and add vendor prefixes.
* [Compatibility](https://tailwindcss.com/docs/compatibility#sass-less-and-stylus) - TailwindCSS v4 Docs
> Sorry for the inconvenience here, however **right now we don't support migrating `.scss` or `.less` files**. Doing so would require us to be able to understand the scss/sass and less syntax to make changes. But even if we do that, Tailwind CSS v4 isn't really compatible with these files anyway. > > I would recommend to see if you can rename the file(s) to `.css` and try again. You might notice that sometimes people use scss for features such as nested css, which should just work already in Tailwind CSS v4 (and modern browsers). So there is a good chance that you might not need `.scss` files at all. > > Again, sorry about the inconvenience here, but if you can migrate to normal `.css` files, then upgrading using the upgrade tool should just work.
* [`tailwindlabs/tailwindcss` #15716 by RobinMalfait:<br>Migration tool doesn't recognize .scss files](https://github.com/tailwindlabs/tailwindcss/issues/15716#issuecomment-2619593290) - GitHub
Simply put, TailwindCSS v4 removes the need for Sass and other preprocessors. The TailwindCSS v4 ecosystem can independently provide the functionality that these preprocessors offered.