This is fine unless you need to center the elements inside this container. To get the x in the middle of these boxes, i used to add padding to the top each time, now with flex you can just add align-items:center and justify-content: center; as seen in the flex example below.
This is much better as you can set the way they align much easier. Also you can use the justify-content: center; to make sure the content is centered, and if you want vertical align center you can use: align-items: center; this seems to have issues if there is more than one element in there.