Detect button::BODY_OUTLINE reliably.

Author: lucaboesch

classes/courseformat/overview.php

@@ -91,10 +91,21 @@ public function get_actions_overview(): ?overviewitem {
 
         $currentanswerscount = $this->manager->count_all_users_answered();
 
+
+        if (
+            class_exists(button::class) &&
+            (new \ReflectionClass(button::class))->hasConstant('BODY_OUTLINE')
+        ) {
+            $bodyoutline = button::BODY_OUTLINE;
+            $buttonclass = $bodyoutline->classes();
+        } else {
+            $buttonclass = "btn btn-outline-secondary";
+        }
+
         $content = new action_link(
             url: new \moodle_url('/mod/questionnaire/report.php', ['instance' => $this->cm->instance]),
             text: get_string('view', 'core'),
-            attributes: ['class' => button::SECONDARY_OUTLINE->classes()],
+            attributes: ['class' => $buttonclass],
         );
 
         return new overviewitem(