Vertical alignment in Bootstrap 4?

Here is a coded example.
The bottom line:
The left column make the direction of the Flex - column class helper d-flex flex-column
You have input in your wrapper, and the unit that should be doing the vertical center of marginy - auto: my-auto, so it will try to occupy a Central position.

https://getbootstrap.com/docs/4.1/layout/grid/#ver...
\rhttps://css-tricks.com/snippets/css/a-guide-to-flexbox/

https://codepen.io/zelenka/pen/wjqPJV?editors=1100 works if you specify the height of the child units