private static function fixShadows($css) {
		$css = preg_replace_callback(self::$patterns['box_shadow'], function ($matches) {
			return $matches[1] . self::flipSign($matches[2]);
		}, $css);

		$css = preg_replace_callback(self::$patterns['text_shadow1'], function ($matches) {
			return $matches[1] . $matches[2] . $matches[3] . self::flipSign($matches[4]);
		}, $css);

		$css = preg_replace_callback(self::$patterns['text_shadow2'], function ($matches) {
			return $matches[1] . $matches[2] . $matches[3] . self::flipSign($matches[4]);
		}, $css);

		$css = preg_replace_callback(self::$patterns['text_shadow3'], function ($matches) {
			return $matches[1] . self::flipSign($matches[2]);
		}, $css);

		return $css;
	}