def split_unit( size )
      m = size.to_s.match(/(\d+)\s*(\D*)/)
      { size: m[1].to_f, unit: m[2] }
    end
def split_unit( size )
      m = size.to_s.match(/(\d+)\s*(\D*)/)
      { size: m[1].to_f, unit: m[2] }
    end
Separate size and unit for easier math.
 Returns: { size: 10, unit: 'px' }