Flexbox option for archive loop to allow centering of last item in a row

The archive loop layouts are based on CSS grid, which means there is no simple way to center the final post in the final row of the layout if it’s, say, #5 of 5 and it’s a four-column grid, so it’s not sitting there all the way to the left, or it it’s the only one returned when the grid is three or four columns. It would be great to have an option to use flexbox here instead of grid so we have more control over centering.