按钮的角半径与下面的视图对齐

There are tons of answers on SO for rounding a particular corner. The issue I'm running into is I'm trying to align a button corner to a rounded corner of the view below. Please see the image. The yellow view is rounded in 4 corners. I'm trying to get the close button to round off at top right to align with the yellow view's round corner. I've used the Swift 3 code below, but the button stays square. Can anyone please point out what is missing?There are tons of answers on SO for rounding a