Bump @webref/css from 6.6.2 to 6.7.1

Bumps [@webref/css](https://github.com/w3c/webref) from 6.6.2 to 6.7.1.
- [Commits](https://github.com/w3c/webref/compare/@webref/[email protected]...@webref/[email protected])

---
updated-dependencies:
- dependency-name: "@webref/css"
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>