CodePen Home fixed aspect-ratio box with container queries
HTML
<div class='parent'>
<div class='aspect-ratio-child'></div>
</div>
CSS
.parent {
display: grid;
container-type: size;
width: min(60em, 90%);
height: min(800px, 50vh);
background: dodgerblue
}
.aspect-ratio-child {
--r: 8/ 5;
place-self: center;
width: min(100cqw, var(--r)*100cqh);
height: min(100cqh, 100cqw/(var(--r)));
background: crimson
}