Gaps between new cabinets are usually filled with slim pieces of trim that match the cabinets and are cut to fit the space.

It can be difficult to find trim pieces to fit into the gaps between existing cabinets. Check the cabinet manufacturer, a home improvement store, or other cabinet companies that might have wood styles that match. If you have an old cabinet that you are removing, you could try to cut a slim piece from that cabinet to use in the slot.

Former builder and instructor of "Save Time and Money in Home Remodeling" cont. ed. course at Emory University