Hi!
The new popups for elements, CSS, JS etc, are all too sensitive on movement.
By this I mean that, in order to close the window, the mouse has to be 100% still. Otherwise the popup can be moved around by dragging the X.
Any situation where the mouse has to go to full stop before a click is quite a cognitive load and frustration, from the UX standpoint. 
This used to happen with elements as well, where a bit harder mouse movement with a click would displace the element. I am not sure if the sensitivity has been tuned in the elements, but if it is not, that would really be a huge thing.
Thanks!