Fix dynamic scss prefix in mixins (#1745)

* Fix dynamic scss prefix in mixins

src/scss/mixins/_mixins.scss

@@ -60,9 +60,9 @@
 
 @mixin focus-ring($show-border: false) {
   outline: 0;
-  box-shadow: 0 0 $focus-ring-blur $focus-ring-width rgba(var(--tblr-primary-rgb), 0.25);
+  box-shadow: 0 0 $focus-ring-blur $focus-ring-width rgba(var(--#{$prefix}primary-rgb), 0.25);
 
   @if($show-border) {
-    border-color: rgba(var(--tblr-primary-rgb), 0.25);
+    border-color: rgba(var(--#{$prefix}primary-rgb), 0.25);
   }
-}
+}