Round corners don't nest

[markwhiting]

Round corners should nest, e.g., bigger round corners should share the center point with smaller ones positioned in them, such as the situation in our scope selector.

It looks like we have a radius of 4 on the inside ones and padding of 8, so the outside ones should be 12, not 16 as they are. I have set the top left in this image to 12 and it looks neater.

[markwhiting]

More generally, we should always do this. Everywhere and forever. haha

[markwhiting]

I think now outside the area also has R = 4, which is not great either. I'd make it so that R_inside + padding = R_outside, such that the round corners of inside and outside share a center point.