update changelog

Author: RobinMalfait

CHANGELOG.md

@@ -29,6 +29,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix negated `content` rules in legacy JavaScript configuration ([#17255](https://github.com/tailwindlabs/tailwindcss/pull/17255))
 - Extract special `@("@")md:…` syntax in Razor files ([#17427](https://github.com/tailwindlabs/tailwindcss/pull/17427))
 - Disallow arbitrary values with top-level braces and semicolons as well as unbalanced parentheses and brackets ([#17361](https://github.com/tailwindlabs/tailwindcss/pull/17361))
+- Extract used CSS variables from `.css` files ([#17433](https://github.com/tailwindlabs/tailwindcss/pull/17433))
 
 ### Changed