Install postcss to solve an error

Author: jasongrout

packages/controls/package.json

@@ -69,6 +69,7 @@
     "karma-webpack": "^5.0.0",
     "mocha": "^9.0.0",
     "npm-run-all": "^4.1.5",
+    "postcss": "^8.3.2",
     "postcss-cli": "^8.3.1",
     "postcss-cssnext": "^3.1.0",
     "postcss-import": "^14.0.2",