change breadcrumb dividers to css variables

src/scss/ui/_breadcrumbs.scss

@@ -23,8 +23,6 @@
 
 @each $name, $symbol in $breadcrumb-variants {
   .breadcrumb-#{$name} {
-    .breadcrumb-item + .breadcrumb-item:before {
-      content: $symbol;
-    }
+    --#{$variable-prefix}breadcrumb-divider: "#{quote($symbol)}";
   }
 }