/// <summary>
        /// Given a string quad, flips the left and right values.
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        static CssValue flipQuad(CssValue value)
        {
            if (!value.IsNumber)
            {
                var parts = value.ToString().Split(' ');

                if (parts.Length == 4)
                {
                    return($"{parts[0]} {parts[3]} { parts[2]} { parts[1]}");
                }
            }

            return(value);
        }