Thanks Craig for your interest!
The div called 'circle' seems only a visual aid.
Looking at the code, there is a <div> called 'homepage-carousel--slide' which contains the slides.
Each slide has a height of 3 times the height of the window and has a large border at the bottom right.
When the user clicks on the next slide, this div 'homepage-carousel--slide-mask' containing the background image is translated upwards until it disappears.
I would like to understand if Greensock can help me manage the animation and if I can also control it with the mousewheel, and which plugins I should need.