title: Container view width decreases after adding safe area constraints
body: <p>I have a <code>ViewController</code> and a container view <code>testcontrollerViewController</code> inside of it. I noticed that after I'm adding constraints to that container view in the storyboard (all the edges match the safe area) its width decreases a little bit, but if I remove constraints width changes back to normal. (Switches from 724px to 712px and back)</p>
  <p>Is it a bug or am I doing something wrong?</p>
  <p><a href="https://i.stack.imgur.com/QzuUk.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QzuUk.jpg" alt="enter image description here" /></a></p>
  <p>I print container view width in its <code>viewDidAppear</code> function.</p>
  <pre><code>class testcontrollerViewController: UIViewController {
  
  override func viewDidLoad() {
      super.viewDidLoad()
      
      
      // Do any additional setup after loading the view.
      
      view.backgroundColor = .red
      print(&quot;container vc load \(testview.frame.width)&quot;)
  }
  
  override func viewDidAppear(_ animated: Bool) {
      print(&quot;container vc appear \(testview.frame.width)&quot;)
      print(&quot;container view safe area insets \(view.safeAreaInsets)&quot;)
  }
  
  @IBOutlet var testview: UIView!
  </code></pre>