Top-margin: auto and flex-grow: 1 don't have any effect

After upgrading from 1.5 beta to 1.5 rc I still have one issue. Have a look at the team cards. I want the red button to push all the way down to the bottom of the box. I tried it by adding top-margin: auto which doesn’t work. I also added flex-grow: 1 to the text field above the button and set the parent element to display: flex. In the inspector the parent element still shows display: block though.
Any idea how I can achieve this? Thanks already.