Fix check for window.CSS

Author: grubersjoe

package.json

@@ -65,6 +65,7 @@
     "eslint-plugin-react-hooks": "^4.6.2",
     "globals": "^15.10.0",
     "jest": "^29.7.0",
+    "jest-environment-jsdom": "^29.7.0",
     "prettier": "^3.3.2",
     "prism-react-renderer": "^2.3.1",
     "react": "^18.3.1",
@@ -88,6 +89,9 @@
     "react": "^18.0.0",
     "react-dom": "^18.0.0"
   },
+  "jest": {
+    "testEnvironment": "jsdom"
+  },
   "browserslist": [
     "last 1 chrome version",
     "last 1 firefox version",