How do I set same height to stack image card block, justify (flexbox) buttons to bottom of cards?

Site URL: https://www.elkowebdesigns.com/services

I feel like I've tried every code I can find online, but I'm not having any luck. I'm trying to get these three buttons to start at the same height - regardless on the content above them (stack image cards). I originally had the buttons as part of the image cards, but wasn't having any luck, they're now separate buttons but I'd be happy to change them back if I could get the code to work. 

Logically, my mind says to set a px height for each block and set the button to margin-top: auto; 

but it isn't working for me. 

password for page is "test"