Bump postcss from 8.5.10 to 8.5.18 in /docs

Bumps [postcss](https://github.com/postcss/postcss) from 8.5.10 to 8.5.18.
- [Release notes](https://github.com/postcss/postcss/releases)
- [Changelog](https://github.com/postcss/postcss/blob/main/CHANGELOG.md)
- [Commits](postcss/postcss@8.5.10...8.5.18)

---
updated-dependencies:
- dependency-name: postcss
  dependency-version: 8.5.18
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/package.json

@@ -48,7 +48,7 @@
     "markdownlint-cli2": "^0.22.0",
     "markdownlint-rule-relative-links": "^5.1.0",
     "oxlint": "1.75.0",
-    "postcss": "^8.5.10",
+    "postcss": "^8.5.18",
     "prettier": "^3.8.0",
     "tailwindcss": "^4.2.1",
     "typescript": "^5.7.3"