border-radius: max(0px, min(8px, calc((100vw - 4px - 100%) * 9999))); → maybe too clever as the line is hard to understand.

and

grid-template-columns: repeat(auto-fit, minmax(min(350px, 100%), 1fr));

This is a great snippet, but there is absolutely zero chance I’m going to remember how to write it every time.

Another trick is to use a toggle value stored in a css variable.