We want to be able to show pop-up notifications. A notification appears and stays visible for three seconds stacking with previous ones. When a notification "disappears" it must first acquire a `hidden` class to allow css transitions to animate it before being completely removed. If the mouse is hovered over a particular notification it should fade back in and not be removed as long as a mouse is moving over it.

See code below (or even better look at source or devtools)