Add stylelint and postcss to devDependencies

package.json

@@ -246,7 +246,7 @@
     "miragejs": "^0.1.40",
     "mock-apollo-client": "^0.7.0",
     "nodemon": "^2.0.4",
-    "postcss": "^7.0.14",
+    "postcss": "^8.4.5",
     "prettier": "2.2.1",
     "prosemirror-schema-basic": "^1.1.2",
     "prosemirror-schema-list": "^1.1.6",
@@ -254,7 +254,7 @@
     "purgecss": "^4.0.3",
     "purgecss-from-html": "^4.0.3",
     "sass": "^1.32.12",
-    "stylelint": "13.9.0",
+    "stylelint": "^14.3.0",
     "timezone-mock": "^1.0.8",
     "vue-jest": "4.0.1",
     "webpack-dev-server": "^3.11.3",