$(function() {
var b = $("#button");
var w = $("#wrapper");
var l = $("#list");
b.click(function() {
w.toggleClass('open'); /* <-- toggle the application of the open class on click */
});
});<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button id="button">Toggle Expand/Collapse</button>
<div id="wrapper">
<ul id="list">
<li>Item</li>
<li>Item</li>
<li>Item</li>
<li>Item</li>
</ul>
</div>#wrapper {
background: #ccc;
overflow: hidden;
transition: max-height 300ms;
max-height: 0; /* <---hide by default */
}
#wrapper.open {
max-height: 100px; /* <---when open, allow content to expand to take up as much height as it needs, up to e.g. 100px */
}