use lower case class names

inc/Ui/Admin.php

@@ -21,7 +21,7 @@ class Admin extends Ui {
      */
     public function show() {
         $this->menu = $this->getPluginList();
-        echo '<div class="UI-admin">';
+        echo '<div class="ui-admin">';
         echo p_locale_xhtml('admin');
         $this->showSecurityCheck();
         $this->showAdminMenu();

lib/tpl/dokuwiki/css/_admin.less

-.dokuwiki div.UI-admin {
+.dokuwiki div.ui-admin {
 
     /* main task grouped in two columns */
     ul.admin_tasks {