I must be overlooking something...

I had this newsletter from CC the other day with a tutorial about creating a nested BS menu from scratch, much like the one we have for similar Foundation menus.
Today I wanted to try this tutorial, and I got it about 95% done, but the wretched dropdown menu will not close on small screens! Either I have done something wrong, or I have missed something, I'm not able to find out what it is. Could someone please take a look?

The attachment contains two files, my effort and the one made by CC. Here is the tutorial:
https://www.coffeecup.com/help/articles … trap-menu/

Display is set to "block" on the "collapse navbar-collapse" container. Choose reset.

Never mind! I found the error. I had applied display: flex; a bit too early.

Yeah, I think we posted at the same time. I rebuilt the thing a couple of times and then it dawned on me