Idea

Inspiration

In the following example, all divs with "child" classes would be the same height, if the JS runtime is included. Could work the same way Container Queries work: CSS ➡ PostCSS ➡ JSON ➡ Runtime

.parent {
    /* styling */
}

.child {
    @equal-height; // or some more interop declaration
}

<div class="parent">
    <div class="child"><!-- content --></div>
    <div class="child"><!-- content --></div>
    <div class="child"><!-- content --></div>
</div>