<style>

div {
    position: absolute;
    top: 0;
    left: 0;
    width: 100px;
    height: 100px;
    background-color: black;

    will-change: rotate;
    rotate: 180deg;

    animation-name: rotate;
    animation-delay: 1000s;
    animation-duration: 1000s;
}

div::after {
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 50%;
    background-color: gray;
}

@keyframes rotate {
    from { rotate: 90deg }
    to { rotate: 90deg }
}
    
</style>
<div></div>
<script src="resources/wait-until-animations-are-committed.js"></script>