interpolate-size: allow-keywords - transition for non-numeric values

Browser support: currently 67%.

@supports (interpolate-size: allow-keywords) {
    :root {
        interpolate-size: allow-keywords;
    }

    details {
        transition: height 0.5s ease;
        height: 2.5rem;

        &[open] {
            height: auto;
            overflow: clip; /* Clip off contents while animating */
        }
    }
}

---

Sources: Chrome Developer, Kevin Powell.