public function styles($style = null, $definition = null)
    {
        if ($style === null && $definition === null) {
            return static::$_styles;
        }
        if (is_string($style) && $definition === null) {
            return isset(static::$_styles[$style]) ? static::$_styles[$style] : null;
        }
        if ($definition === false) {
            unset(static::$_styles[$style]);

            return true;
        }
        static::$_styles[$style] = $definition;

        return true;
    }