code: def set_left_margin(self, left_margin):
          
          self.__header.style.margins.left = left_margin
          self.__prologue.style.margins.left = left_margin
          self.__items_section.style.margins.left = left_margin
          self.__epilogue.style.margins.left = left_margin
          self.__footer.style.margins.left = left_margin
          self.__prompt.style.margins.left = left_margin
          return self
docs: Set the left margin of the menu.  This will determine the number of spaces between the left edge of the
          screen and the left menu border.
          :param left_margin: an integer value