Great idea, although it is quite inconvenient that you have to tap/swipe to show the modern version (at least on mobile). Makes it difficult to compare.
As others have stated, there is no point in a "reveal". Simply show the comparison upfront. User interaction should not be necessary as it only needs to be a plain old html document. You didn't need to write any script. When I got through a bit of it, I wasn't sure if I accidentally skipped something or missed a nuance.
Maybe `ArrowLeft`/`ArrowRight` or `j`/`k` to flip through all of card pairs? Or just allow us to scroll through all the pairs. In either case, both old and new should be visible.
For a better visualization to compare old/new, just click on the card and it will open that particular pattern in a new page.