A CSS only horizontal scrolling full screen 'stacking' slideshow that works on PC using the mousewheel (or horizontal scrollbar), and on tablets and mobiles using left/right swipe.
For Chrome, Opera and Edge on PCs just make one quick swipe of the mousewheel and wait for the browser to scroll in each image.
Firefox and iOS Safari scroll-snap and sticky bug now 'fixed' using my method 29th October 2021. This is a known bug that has been around for over 2 years Firefox Bug 1594386.