Say, you have 4 items, and there is only room for 3 items per row. Where would the last item appear? Centered or to the left? Your flexbox props make me think that it would be in the center. But then, it’s not a real grid, is it? ;)
If I am assuming correctly, do you have any clever ideas on how to do that (make the last item go to the left) and still benefit from the benefits of justifyContent values like 'center' and 'space-between'?