private function classes() : string
    {
        $classes = '';

        if ($this->xl_size !== null) {
            $classes .= ' col-xl-' . $this->xl_size;
        }

        if ($this->lg_size !== null) {
            $classes .= ' col-lg-' . $this->lg_size;
        }

        if ($this->md_size !== null) {
            $classes .= ' col-md-' . $this->md_size;
        }

        if ($this->sm_size !== null) {
            $classes .= ' col-sm-' . $this->sm_size;
        }

        if ($this->xs_size !== null) {
            $classes .= ' col-' . $this->xs_size;
        }

        if ($this->bg_color !== null) {
            $classes .= ' bg-' . $this->bg_color;
        }

        if ($this->text_color !== null) {
            $classes .= ' text-' . $this->text_color;
        }

        return trim($classes);
    }