Hey RTX,
It’s going to take a little coding, but it’s definitely doable (of course, cause it’s done there).
What I’m thinking is that in each of those repeater boxes, at the bottom, there’s an invisible (colour set to transparent) object which has an onViewportEnter and an onViewportLeave event handler attached to it.
Then it calls the new hide and show functions to give that nice fadeIn/fadeOut effect. A warning though. The Javascript on Wix is not very responsive, so you’ll have issues with persons who scroll up and down too quickly. They will end up with missing boxes in the repeater.