With modal on top of side modal form, second overlay does not cover side modal #2564
Description
This affects confirm nav on side modal form as well as the image upload form. Demo video from #2328 (comment) shows the approach of simply turning off the overlay for the second modal. But for image upload this feels less good because the modal is up for a while and there's a lot going on in both the upload modal and the side modal form. So the better fix would be to show the overlay but give it a higher z-index when it's on top of the side modal so that it can cover the side modal form as well. Now that I write this out, it occurs to me that it might work to simply always give the modal and its overlay that high z-index.