simple theme: upgrade some of dependencies

* less-plugin-clean-css: no updated version.
  @wikipedia/less-plugin-clean-css might be an alternative.

* stylelint & stylelint-config-standard
  the new versions require configuration and source code changes

package.json

@@ -1,6 +1,6 @@
 {
   "dependencies": {
-    "eslint": "^8.7.0",
+    "eslint": "^8.11.0",
     "pyright": "^1.1.215"
   }
 }