Summary: Enable fine-tuning corners, on top of the existing border-radius, by specifying the shape/curvature of the corner. This allows shapes like squircles, notches, scoops etc., and animating between them.
Intent: https://groups.google.com/a/chromium.org/g/blink-dev/c/UKLLVghiHYQ/m/tv0ANlToEQAJ
Spec: https://drafts.csswg.org/css-overflow-5/#scroll-navigation
Explainer: https://flackr.github.io/carousel/
Other Resources:
=== This is a demo of CSS ::scroll-button() and ::scroll-marker() ===