Arghh, those floating Safari windows. How do you get rid of them?
Then press the Safari icon (or alternatively, press and hold on the Safari icon and choose "Show All Windows").
Now, all of those floating Safari windows are shown, and you can "toss them away" and close them.
Yes, it's not a very intuitive discovery process :(
Considering Exposé and its default gestures exist on MacOS, you'd think maybe they'd take cues from that?