I remember with great displeasure the bad old days of creating a 3x3 table for every container and jamming a rounded corner gif into each of the four corners to create this effect.
I dunno, I look back on the <table>-based layout days with fondness, probably because I was young and the Web was nothing but rolling green fields and endless potential. I didn't see the limitations, only the opportunities for inventiveness. I'll never feel the same satisfaction as I did when those first few website designs came together.
In games you had to do this 9 piece slice, one slice for each of the 4 corners, all 4 straight sides that can be repeated as a pattern and the middle background piece
Nine-patch image scaling[0] is still a thing, and is only orthogonally related to setting a border radius (it's a hell of lot more versatile than that).
Do you not remember a time before border-radius? Or -webkit-border-radius? I remember including a premade rounded rectangle button in Flash just to get that visual effect.
To be fair, the original comment said other platforms should add this, and border-radius has been widely supported for at least 15 years. You'd have to look hard for a browser that needs it to be added.
It was only when I later re-read the comment I replied to, with the part about Bill Atkinson not knowing about the border-radius feature in CSS, that I realized what was going on.
At least I hope my note about the pixelated icons may have been of interest to a few.
Not only on macos, on the hardware as well. Macbook that I'm typing this comment on has a screen with rounded corners on top, and it just feels better than right angles on the bottom.
That effect is 100% done in software. Full black on screens is just really good now. If you don’t believe me look at a photo in full screen while zoomed in.
I'm not sure that's true that it's (always) done in software. For example, the newest Framework Laptop 13 has higher resolution screens that come with rounded corners, because whatever supplier had a large stock of them lying around. If it was just software, the concept of having a "rounded corner screen" from a supplier wouldn't exist.
I'm pretty sure it's a screen cutout - the corners are still rounded when fullscreen zooming, and on asahi linux. There's also another cutout for the notch at the top of the screen. Also, it's not a great panel and the blacks aren't very good - you can still see light coming from the monitor with a full back image in fullscreen and it changes based on brightness.
So if it is software, then it's very low level and with darker blacks than anything else on screen, and has a super tiny bezel right at the corner. I'm pretty sure it's a cutout.
other platforms should add more of this.