The motivation here is Use attention-attracting cue when pressing Ctrl+F while in the find bar and do "something" to call attention to the widget. I thought I'd try some of the built-in GTK CSS support. So here we animate the widget to reduce its left and right margins inwards a little and its opacity to 50% before returning to its original properties.
Nothing is ever simple, so in order to repeat the animation (the second time ctrl+f is pressed while the widget has focus) we have to duplicate the animation and use the other copy when the previous copy was last run.
