title: When using a custom transition, why does the UIDropShadowView inset the presenting view controller?
body: <p>I am writing a basic custom transition with swift. My issue is that the transition is insetting the presenting view controller with rounded corners for some reason. Why is this happening, and is it possible to disable it?</p>
  
  <p><a href="https://i.stack.imgur.com/HIL62.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/HIL62.gif" alt="custom_transition"></a></p>
  
  <p>Presenting view controller:</p>
  
  <pre><code>final class ViewController: UIViewController {
  
      let card = UIView()
  
      override func viewDidLoad() {
          super.viewDidLoad()
  
          view.addSubview(card)
          card.heightAnchor == 200
          card.horizontalAnchors == view.horizontalAnchors + 24
          card.centerAnchors == view.centerAnchors
  
          card.backgroundColor = .black
          card.layer.cornerRadius = 8
  
          view.backgroundColor = .white
  
          card.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(presentView)))
  
      }
  
      @objc func presentView() {
  
          let detail = DetailViewController()
          detail.transitioningDelegate = self
          present(detail, animated: true, completion: nil)
  
      }
  }
  
  extension ViewController: UIViewControllerTransitioningDelegate {
      public func animationController(forPresented presented: UIViewController,
                                      presenting: UIViewController,
                                      source: UIViewController) -&gt; UIViewControllerAnimatedTransitioning? {
          return CardModalPresentAnimator()
      }
  }
  </code></pre>
  
  <p>Presented view controller:</p>
  
  <pre><code>final class DetailViewController: UIViewController {
      override func viewDidLoad() {
          super.viewDidLoad()
          view.backgroundColor = .red
      }
  }
  </code></pre>
  
  <p>Custom Transition:</p>
  
  <pre><code>final class CardModalPresentAnimator: NSObject, UIViewControllerAnimatedTransitioning {
  
      func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -&gt; TimeInterval {
          return 0.4
      }
  
      func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
  
          guard
              let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) as? ViewController,
              let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as? DetailViewController
              else { return }
  
          let containerView = transitionContext.containerView
          containerView.insertSubview(toVC.view, aboveSubview: fromVC.view)
          toVC.view.frame = fromVC.card.frame
  
          UIView.animate(withDuration: transitionDuration(using: transitionContext), animations: {
              // center the modal on the screen
              toVC.view.frame = UIScreen.main.bounds
          }, completion: { _ in
              transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
          })
      }
  }
  </code></pre>