Helpo de LibreOffice 24.8
To hide column and line headers in a table:
Under the menu item LibreOffice - PreferencesTools - Options - LibreOffice Calc, go to the View tab page. Unmark Column/row headers. Confirm with OK.
To hide grid lines:
Under the menu item LibreOffice - PreferencesTools - Options - LibreOffice Calc, go to the View tab page. Choose Hide in the Grid lines dropdown. Confirm with OK.