<!DOCTYPE html>
<style>
div {
width: 100px;
height: 100px;
background-color: red;
}
.animate {
animation-name: test;
animation-duration: 4s;
}
@keyframes test {
from { opacity: 0.0;}
to { opacity: 1.0;}
}
</style>
<div id="target" class="animate"></div>;