Custom images for moderator in bbpress

Hi I’m really sorry to open another one for this topic but I really can’t figure out how to add this.
Custom images for moderator or key master replies in bbpress. I tried adding the CSS you provided here:
https://kriesi.at/support/topic/custom-images-for-moderator-in-bbpress/

But no matter where I put it it does not change anything. Where is this CSS suppose to go? Custom CSS, bbpress_mod?
I also tried adding

add_filter('bbp_get_reply_class','add_extra_forum_class',10,2);
function add_extra_forum_class($classes, $id)
{
	global $post;
	$authordata = get_userdata( $post->post_author );

	if(isset($authordata->allcaps) && !empty($authordata->allcaps['delete_others_replies']))
	{
		$classes[] = 'moderator';
	}

	return $classes;
}

But not even this effects the page. When inspecting the reply div nothing changes.

Thanks in advance,
Marcel