title: How do I get button shadow working with Swift 4.2?
body: <p>I am trying to get my button to render a shadow in swift 4.2</p>
  
  <p>I've followed other examples to no avail.  What am I missing?</p>
  
  <pre><code>import UIKit
  
  class ViewController: UIViewController {
  
  @IBOutlet weak var btnHi: UIButton!         // Standard button tweeked in view controller
  @IBOutlet weak var btnNext: NextButton!     // My custom button via class
  
  override func viewDidLoad() {
      super.viewDidLoad()
      // Do any additional setup after loading the view, typically from a nib.
  
      btnHi.layer.cornerRadius  = btnHi.frame.height / 2
      btnHi.layer.borderWidth   = 3.0
      btnHi.layer.borderColor   = UIColor.darkGray.cgColor
  
      btnHi.layer.shadowColor   = UIColor.black.cgColor
      btnHi.layer.shadowOffset  = CGSize(width: 0.0, height: 6.0)
      btnHi.layer.shadowRadius  = 8
      btnHi.layer.opacity       = 0.5
      // btnHi.clipsToBounds       = true
      // btnHi.layer.masksToBounds = false
  }
  
  @IBAction func btnNext(_ sender: Any) {
      btnNext.setupShakeButton()
  }
  
  }
  </code></pre>
  
  <p>should see a drop shadow for the button instead I get no shadow.
  <a href="https://i.stack.imgur.com/1wwBk.png" rel="noreferrer"><img src="https://i.stack.imgur.com/1wwBk.png" alt="enter image description here"></a></p>