How to remove the lines that are present in the Column Headers with in a Table?

I  need to remove  the line which is present in the column headers.

Please find the attached screen shot.

I am trying to edit in CSS   as below::

.sapUiTableColRsz  #__column1-rsz{

/*  border-left: none !important;  */

  /* visibility : hidden !important; */

  border-collapse: collapse; !important;

}

Please do guide me in achieving this.

Thanks in advance:)