fix: invalid theme function error that stylelint needs to know about

```
resources/scss/components/_global-buttons.scss
  54:62  ✖  Unexpected unknown function "theme"  function-no-unknown
  72:62  ✖  Unexpected unknown function "theme"  function-no-unknown
```

.stylelintrc

@@ -10,6 +10,11 @@
             ]
         }],
         "no-invalid-double-slash-comments": null,
-        "selector-class-pattern": null
+        "selector-class-pattern": null,
+        "function-no-unknown": [ true, {
+            "ignoreFunctions": [
+                "theme"
+            ]
+        }]
     }
 }