def document_style_by_id(id)
      root_object.document_styles.each do |style|
        return style if style.style_id == id
      end
      nil
    end
def document_style_by_id(id)
      root_object.document_styles.each do |style|
        return style if style.style_id == id
      end
      nil
    end
Return document style by its id
 @param id [String] id of style
 @return [DocumentStyle, nil]