SwiftUI Mask a rectangle inside a rounded rectangle

Hello there. I am wondering, in SwiftUI, how do you mask the contents of a rounded rectangle so that a child rectangle clips the corners.

In my example I have a white rounded rectangle and a pink rectangle on a zstack, I've tried to apply clipping, but the pink rectangle does not conform to the corners.

I've tried applying .mask to the white rectangle, but it gives different results to expectations (sometimes it doesn't show the pink rectangle).

I did find an example where you can set your own cornerRadius Round Specific Corners SwiftUI

But I was wondering if perhaps there was a way to mask the internals/body of the pink rectangle so that it conforms to the parent's rounded rectangle?

My code follows;

var body: some View {
        GeometryReader { geometry in

            Color.gray
                .edgesIgnoringSafeArea(.top)
                .overlay(

                    ZStack (alignment: .topLeading) {

                        RoundedRectangle(cornerRadius: 16,
                                         style: .continuous)
                            .foregroundColor(.white)
                            .shadow(radius: 10)
                             // Tried using .mask here 

                        Rectangle()
                            .fill(Color.pink)
                            .frame(minWidth: 0, maxWidth: .infinity, maxHeight: 150, alignment: .top)
                            .clipped()


                    }
                    .frame(width: 300, height: 450, alignment: .center)
            )

        }
        .edgesIgnoringSafeArea(.all)
    }

Edit: To clarify:

The pink rectangle should remain as a rectangle, but clip the top left and right to match the parent white rounded rectangle.

If I correctly understood your goal, here is a solution - the only needed clip in right place is after internal content (two rectangles in this case) is constructed. So clipping with RoundedRectangle gives rounded corners around entire card. (As well as shadow most probably is needed to entire card, so placed at the end).

UPDATE: re-tested with Xcode 13.3 / iOS 15.4

ZStack (alignment: .topLeading) {
    Rectangle()
        .foregroundColor(.white)

    Rectangle()
        .fill(Color.pink)
        .frame(minWidth: 0, maxWidth: .infinity, maxHeight: 150, alignment: .top)
}
.clipShape(RoundedRectangle(cornerRadius: 16))       // << here !!
.frame(width: 300, height: 450, alignment: .center)
.shadow(radius: 10)