scrollViewDelegate.swift

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        // get the content offset for y-axis
        let contentOffsetheight = scrollView.contentOffset.y
        //if the value is negative
        if contentOffsetheight < 0 {
            //change the anchors
            contentViewTopAnchor.constant   = contentOffsetheight
            headerViewHeightAnchor.constant = 450 + (-contentOffsetheight)
        }
    }