css hide animation
div {
border: 1px solid #eee;
}
div > ul {
visibility: hidden;
opacity: 0;
transition: visibility 0s, opacity 0.5s linear;
}
div:hover > ul {
visibility: visible;
opacity: 1;
}
<div>
<ul>
<li>Item 1</li>
<li>Item 2</li>
<li>Item 3</li>
</ul>
</div>