Initially, it pops open a little pop-up with a grey box and a Summarize button. It was not at all clear to me that I was then expected to manually click the “Summarize” button again to make it actually summarize.
Once I did that, it generated a summary. The summary appeared in a little box with
--modal-max-width: 47em, much too small to show the actual summary.
The summary is about 100 words long. For a few hundred words of text, I think this modal should be larger, and/or not a modal at all.