Center incomplete bottom row in a three column simple list

On my three column People page, I would like the content items in the  last row of less than 3 columns to be centered across the full three columns as well as the two column breakpoint. Can someone help me with this code, which I assume would be injected in the header. Thank you!

https://javelinbiotech.com/team-2

Password=team2

Thank you so much for your help!