title: Animate the overflow property
body: <p>I need to animate height, and set <code>overflow: hidden</code> for the first keyframe, and <code>overflow: visible</code> (and keep it) for the last one.</p>
  
  <p>I'm trying this, but at the end, <code>overflow</code> is still <code>hidden</code>.</p>
  
  <p>How can I solve this issue?</p>
  
  <p>The 2 includes are merely SCSS polifill mixins.</p>
  
  <pre><code>@include keyframes(open) {
    0% {
      height: 0;
      overflow: hidden;
    }
    100% {
      height: $main_menu_height;
      overflow: visible;
    }
  }
  
  
  #main-menu-box {
      overflow: hidden;
      height: 0;
  
      &amp;.opened{
         @include animation('open 200ms ease-out 0s 1 normal forwards');
      }
  }
  </code></pre>