public static function addCustomSubmitBtn($tag)
    {
        $tag = new FormTag($tag);

        $class = wpcf7_form_controls_class($tag->getType());

        $atts = [];

        $atts['class'] = $tag->get_class_option($class).' btn';
        $atts['id'] = $tag->get_id_option();
        $atts['tabindex'] = $tag->get_option('tabindex', 'int', true);

        $value = isset($tag->values[0]) ? $tag->values[0] : '';

        if (empty($value)) {
            $value = __('Send', 'contact-form-7');
        }

        $atts['type'] = 'submit';
        $atts['value'] = $value;

        $atts = wpcf7_format_atts($atts);

        $html = sprintf('<button type="submit" %1$s>%2$s</button>', $atts, $value);

        return $html;
    }