You can override align-items with align-self for a flex item.
I am looking for a way to override justify-content for a flex item.
AFAIK there is no property for that in the specs, but here is a trick I’ve been using:
set the container element ( the one with display:flex ) to justify-content:space-around
Then add an extra element between the first and second item and set it to flex-grow:10 (or some other value that works with your setup)
Edit: if the items are tightly aligned it's a good idea to add flex-shrink: 10; to the extra element as well, so the layout will be properly responsive on smaller devices.