I wasn't even aware that the Mac existed at the time, but I always had a fondness for rounded rectangles because the Amstrad CPC character set had 16 characters

I wasn't even aware that the Mac existed at the time, but I always had a fondness for rounded rectangles because the Amstrad CPC character set had 16 characters that represented all possible combinations of a central dot with N, E, S, W spokes. They were rounded for the 4 cases that represented 90 degrees, and the rounded rectangle look was perfect for using as borders around things. This was 1984, so wouldn't have been long after the original Mac but was maybe influenced by it. As far as I know, no other 8-bit computers have rounded container characters like this. I later used PCs, and the CGA text mode had its nice 1/2 line variants, which were good for variety, but they were square so I never found them as appealing as the rounded ones I knew from the Amstrad.