Issue #3158794: Drupal 9 - Error: [MixItUp] The provided selector yielded no container element

css/mixitup_views.css

@@ -47,3 +47,7 @@ html.js .sort_wrapper .sort.desc:after {
 html div[id^="MixItUp"] {
   padding-bottom: 20px;
 }
+
+html.js .filters_wrapper .mixitup_views_filter_buttons.active {
+  filter: brightness(85%);
+}