WebUI: revise lint rules for css

Some rules are already covered by other tools, so remove them.

src/webui/www/stylelint.config.mjs

@@ -5,15 +5,12 @@ export default {
     ],
     ignoreFiles: ["private/css/lib/*.css"],
     rules: {
-        "color-hex-length": null,
+        "color-hex-length": "long",
         "comment-empty-line-before": null,
         "comment-whitespace-inside": null,
-        "function-name-case": null,
-        "length-zero-no-unit": null,
         "no-descending-specificity": null,
         "order/properties-alphabetical-order": true,
         "selector-class-pattern": null,
         "selector-id-pattern": null,
-        "value-keyword-case": null
     }
 };