Issue #3382654 by Grimreaper: There is no btn-default button on Bootstrap 5

src/HookHandler/PreprocessMenuLocalAction.php

@@ -25,7 +25,7 @@ class PreprocessMenuLocalAction {
 
     if (isset($link['url'])) {
       // Turn link into a mini-button and colorize based on title.
-      $class = Bootstrap::cssClassFromString($link['title'], 'default');
+      $class = Bootstrap::cssClassFromString($link['title'], 'outline-dark');
       if (!isset($options['attributes']['class'])) {
         $options['attributes']['class'] = [];
       }