LibreOffice 25.2 Help
To permanently hide column and line headers in a table:
Under the menu item Tools - Options - LibreOffice Calc, go to the View tab page. Unmark Column/row headers. Confirm with OK.
To hide grid lines:
Under the menu item Tools - Options - LibreOffice Calc, go to the View tab page. Unmark Column/row headers. Confirm with OK.