Trouble with CSS Image Layout

I’m currently working on the portfolio project page. I’m trying to make two columns of three photos centered in the page, but I can’t figure out why my code isn’t working. Any suggestions would be appreciated!

I had to take the height property out because the images didn’t stay in the container, but otherwise your code fixed my problem. I didn’t know you could use the text-align property for things other than text. Thanks!

I updated the codepen and here’s a screenshot

I’m also using the latest version of chrome, but I’m running mac OS. I feel like that shouldn’t make a difference though, I’m really curious to know why.