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function carbon_tag_cloud_class_active($tags_data) {

	$body_class = get_body_class();

	foreach ($tags_data as $key => $tag) {
		if(in_array('tag-'.$tag['id'], $body_class)) {
			$tags_data[$key]['class'] =  $tags_data[$key]['class'] ." active-tag";
		} 
	}

	return $tags_data;
}

add_filter('wp_generate_tag_cloud_data', 'carbon_tag_cloud_class_active');