It's all over the place. E.g.: https://www.apple.com/v/iphone-duo/a/images/overview/highlig... - the bottom left corner, or the search icon here: https://www.apple.com/v/iphone-duo/a/images/overview/product... , https://www.apple.com/v/iphone-duo/a/images/overview/shared-... and so on.

Of course, some of it is just the usual Apple stupidity and ineptness in the UI design (that infected the whole industry): https://www.apple.com/v/iphone-duo/a/images/overview/shared-...

But rounded corners certainly did not help.