Modal Animation issue

Question

I am trying to get a modal animating with Tweenmax. It currently animates but the issue I am having is that I want it to animate from the top of the screen to the middle and stop there. Currently, it just animates into the middle.

HTML:

<button onclick="clickButton();">Testing</button>
<div id="container">
  <div class="background">
    <div class="modal">
      <h2>Testing Modal</h2>
      <p>Testing.</p>
    </div>
  </div>
</div>

JS:

clickButton = function() {
  TweenMax.to("#container", 0.3, {
    className: "+=active",
    ease: Power1.easeOut
  });
};

I have tried using CSS to do this:

#modal-container .modal-background {
  display: table-cell;
  background: rgba(0, 0, 0, 0.8);
  text-align: center;
  vertical-align: top;
}
#modal-container.active .modal-background {
    vertical-align: center;
}

Codepen

Answer 1

Change your transform like this

#container.active {
    transform: translateY(100%);
}

And your #container position top and left

#container {
    position: fixed;
    display: table;
    height: 100%;
    width: 100%;
    top: -100%;
    left: 0;
    z-index: 1;
}

Its may help you, here's my code for your issue Codepen