How do I center grid content?

I have speakers listed on my site in a grid format. When I have 6 speakers, the grid looks amazing...however I'll only have five this month and it's really bothering me that the two on the bottom aren't centered (the fact that all of the Linkedin buttons are at a different height is a different issue!). I've gone through all of the settings/ options I could find with no luck. Anyone know how to do this?

https://www.cometorecess.com/

Add to Design > Custom CSS

@media screen and (min-width:768px) {
.user-items-list-item-container[data-section-id="645289734e3f29179840ce26"] li:nth-child(n+4) {
    position: relative;
    left: calc(~"50% + 30px");
}
}