Hello @Rodrigo,
thank you very much for your answer.
I just realized that I must have formulated my initial issue description wrong becasue this conversation is going in the wrong direction (that is not a criticism, just honest observation). English language is not my native language, so I think what make perfect sense to me in my head doesn't translate that well on the paper ? ? ? and I'm trully sorry for that.
The animations are working fine for me, they are not the issue. I also now understand better your initial solution to my problem - I am not trying to change nor animate the physical height of the slides' (in the initial example: 'slide-0', 'slide-1', 'slide-2'). What I'm having trouble with is adjusting the (what I call) scroll height without changing the physical height of the DOM element (attached image shows the desired behaviour). I would like to 'push' the end trigger and start trigger for next slide further down, so it would be, let's say, 125% of the slide's actual height. And updating the 'bottom' parameter for the slides messes up the whole structure for me (as seen in my first post's codepen).