<style>
body {
    display: grid;
    grid-template-columns: 100px 50px;
}
div {
    container-type: inline-size;
    background-color: blue;
}
span { background-color: red }
@container (width = 100px) {
    span { background-color: green }
}
</style>
<body>
<div>
    <span>1</span>
</div>
<div>
    <span>2</span>
</div>
</body>