Use stylelint for CSS linting

src/webui/www/.stylelintrc.json

@@ -0,0 +1,18 @@
+{
+  "extends": "stylelint-config-standard",
+  "plugins": [
+    "stylelint-order"
+  ],
+  "rules": {
+    "color-hex-length": null,
+    "comment-empty-line-before": null,
+    "comment-whitespace-inside": null,
+    "declaration-colon-newline-after": null,
+    "function-name-case": null,
+    "indentation": 4,
+    "length-zero-no-unit": null,
+    "no-descending-specificity": null,
+    "value-keyword-case": null,
+    "order/properties-alphabetical-order": true
+  }
+}

src/webui/www/package.json

@@ -7,12 +7,15 @@
   },
   "scripts": {
     "format": "js-beautify private/*.html private/scripts/*.js private/views/*.html public/*.html public/scripts/*.js && prettier --write **.css",
-    "lint": "eslint private/*.html private/scripts/*.js private/views/*.html public/*.html public/scripts/*.js"
+    "lint": "eslint private/*.html private/scripts/*.js private/views/*.html public/*.html public/scripts/*.js && stylelint **/*.css"
   },
   "devDependencies": {
     "eslint": "*",
     "eslint-plugin-html": "*",
     "js-beautify": "*",
-    "prettier": "*"
+    "prettier": "*",
+    "stylelint": "*",
+    "stylelint-config-standard": "*",
+    "stylelint-order": "*"
   }
 }