public function getOffsetClassNames(DBViewports $offset = null)
    {
        $classes = [];
        
        if (!$offset) {
            $offset = $this->owner->getOffsetViewports();
        }
        
        foreach ($offset->getViewports() as $viewport) {
            $classes[] = $this->getOffsetClass($viewport, $offset->getField($viewport));
        }
        
        return $classes;
    }