public function addStyle($name, $properties)
    {
        $style = $this->createElement('ss:Style');
        $style->setAttribute('ss:ID', $name);
        $this->styles->appendChild($style);
        $font = $this->createElement('ss:Font');
        $style->appendChild($font);
        foreach($properties as $prop=>$val){
            $font->setAttribute('ss:'.$prop, $val);
        }
        return $style;
    }