https://github.com/learn-swift/RoundShadowView

AddShadowAndRoundedCorners.swift

private var shadowLayer: CAShapeLayer!
private var cornerRadius: CGFloat = 25.0
private var fillColor: UIColor = .blue // the color applied to the shadowLayer, rather than the view's backgroundColor
 
override func layoutSubviews() {
super.layoutSubviews()
if shadowLayer == nil {
        shadowLayer = CAShapeLayer()
        shadowLayer.path = UIBezierPath(roundedRect: bounds, cornerRadius: cornerRadius).cgPath
        shadowLayer.fillColor = fillColor.cgColor
        shadowLayer.shadowColor = UIColor.black.cgColor
        shadowLayer.shadowPath = shadowLayer.path
        shadowLayer.shadowOffset = CGSize(width: 0.0, height: 1.0)
        shadowLayer.shadowOpacity = 0.2
        shadowLayer.shadowRadius = 3
        layer.insertSublayer(shadowLayer, at: 0)
    }
}

// Full example: https://github.com/learn-swift/RoundShadowView