CSS Height Transition Not Animating - css

Question

I have a div, agent-list which has the classes open and closed set on it via Javascript. In Chrome and Firefox, the animation is not working - the div is immediately resized. I am 99% sure this code worked previously and I don't see anything wrong with it.
.agent-list {
position: absolute;
z-index: 20;
bottom: 0;
background-color: $lightGrey;
transition: all 1.15s;
transition-timing-function: ease-in;
&.closed {
height: 48px;
}
&.open {
height: 400px;
overflow-y: auto;
}
}

Answer 1

Please check the solution.
$(function(){
$('button').on('click', function(e){
e.preventDefault();
$('.agent-list').toggleClass('open');
});
});
body{
position: relative;
margin: 0;
padding: 0;
height: 100%;
width: 100%;
}
.agent-list {
position: absolute;
z-index: 20;
top: 50px;
background-color: #565656;
transition: height 0.3s ease-in-out 0s;
height: 48px;
left: 0;
overflow: hidden;
width: 100%;
color: #ffffff;
}
.agent-list.open {
height: 400px;
overflow-y: auto;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<button type="button">Click ME</button>
<div class="agent-list">
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Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.
</div>

Answer 2

It is working fine in the fiddle I just made. I suppose your problem is in the JS.
Mine is
document.getElementById("MyElement").className = "agent-list closed";
https://jsfiddle.net/swmfowgp/

Answer 3

As it turns out, the CSS is fine, and the React code was creating a different div for .open and .close. When I fixed that to use the same div and toggle the class, it worked.