Flexbox: .follow-btn set to display: flex - why?

I’m doing the CSS Flexbox: Apply the flex-direction […] exercise and I’m able to do it, but I don’t understand why the follow button div is set to display: flex. Looking at the html, there is only one child element in the div with class “follow-btn”, so why does that one element (the button) need to flex? If I toggle “display: flex” off of the .follow-btn selector, the height of the button changes. I’d really like to understand why a parent with only one child would be set to flex. Any sage words of wisdom would be much appreciated!