`@apply` No Longer Works in `.less` Files After Upgrading to Tailwind CSS v4

[saeidi-dev]

Describe the bug
After upgrading from Tailwind CSS v3 to v4, all @apply directives inside .less files are broken. The build fails and styles are not applied.

Environment

• Tailwind CSS: v4.x
• Previous version: v3.x
• Preprocessor: Less

To Reproduce

1. Have a project using Tailwind CSS v3 with .less files containing @apply
2. Upgrade to Tailwind CSS v4
3. Run the build
4. Observe errors related to @apply not being recognized in .less files

Expected behavior
@apply should work in .less files as it did in v3, or a clear migration path should be provided.

Current behavior
Build fails with errors. @apply directives inside .less files are not processed by Tailwind v4.

Additional context
I have a large codebase with many .less files heavily using @apply. Migrating all of them is a significant effort.

Question
What is the recommended migration path for projects using @apply inside .less files?
Is there any workaround or compatibility layer planned for v4?

I understand that v4 is designed as a standalone CSS build tool and is not intended to be used alongside preprocessors like Less or Sass. However, a migration guide or an automated upgrade tool that handles .less files would be greatly appreciated.