public function setStyle($key, $value)
    {
        foreach ($this as $node) {
            if ($node instanceof \DOMElement) {
                /** @var \DOMElement $node */
                $styles = Helpers::cssStringToArray($node->getAttribute('style'));
                if ($value != '') {
                    $styles[$key] = $value;
                } elseif (isset($styles[$key])) {
                    unset($styles[$key]);
                }
                $node->setAttribute('style', Helpers::cssArrayToString($styles));
            }
        }
        return $this;
    }