Corvid video that Wix provided is unclear

I was watching the video from Corvid
https://www.wix.com/corvid/tutorial/how-to-add-custom-interactions-with-javascript
4:40 of the video
I understand the expansion, but the collapse does not explain how to down arrow get invisible so the up arrow is exposed to click.
That is the one detail that is unclear from this entire section.
Can someone explain it to me?

Thank you!