CSS - grid-column: How can I use only half the space for a column?

I'm now working on a calculator made with HTML. For the buttons, I use the CSS grid to arrange them in 4 columns. Since I don't want to do much coding afterwards, I use two separate Buttons for the "()" brackets.

Each button takes inter 1/4 of the screen width. The buttons for the bracket are supposed to be half as wide, i.e.: 1/8 of the screen width, so together, they'd only take 1/4.

My problem is that I don't know how to get them together because they leave a "1/8 screen width"-gap.

It would be great if someone could tell me how to get rid of the gap using only CSS.

Thank you in advance