<!DOCTYPE html>
<link rel="help" href="https://drafts.csswg.org/css-backgrounds-3/#background-color">
<style>
@keyframes bgcolor {
  0% { background: Field; }
  100% { background: green; }
}
.target {
  animation: bgcolor 50ms;
  width: 100px;
  height: 100px;
}
</style>
<div class="target"></div>