title: Weird animation behavior using Swift 4 and UIView
body: <p>I really can't figure out what's wrong with my code. Let me explain in detail what was my aim:</p>
  
  <ul>
  <li>I have two <code>UIView</code> in the same <code>UIViewController</code>. They're called "<code>redSquare</code>" and "<code>greenSquare</code>".</li>
  <li>When the <code>UIViewController</code> is presented I want to animate the <code>redSquare</code> in order to move on the Y-axis till it reaches the top-border of the <code>greenSquare</code>.</li>
  </ul>
  
  <p>This is how I set the xCode project:</p>
  
  <p><a href="https://i.stack.imgur.com/pSOf8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/pSOf8.png" alt="enter image description here"></a></p>
  
  <p>The behavior that I got is completely the opposite and I really can't understand why and what's happening:</p>
  
  <p><a href="https://i.stack.imgur.com/zluTI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/zluTI.png" alt="enter image description here"></a></p>
  
  <p>Any tips or explanations for this?</p>