Bonafide CSS trick alert! Nelson Menezes figured out a new way (that only works in Firefox for now) that is awfully clever.
Perhaps you know that CSS cannot animate to auto dimensions, which is super unfortunate. Animating from zero to “whatever is necessary” would be very helpful very often. We’ve documented the available techniques. They boil down to:
- Animate the
max-heightto some more than you need value, which makes timing easing imprecise and janky. - Use JavaScript to measure the final size and animate to that, which means… using JavaScript.
Nelson’s technique is neither of those, nor some transform-based way with visual awkwardness. This technique uses CSS Grid at its core…
.expander {
display: grid;
grid-template-rows: 0fr;
transition: grid-template-rows 1s;
}
.expander.expanded {
grid-template-rows: 1fr;
}Unbelievably, in Firefox, that transitions content inside that area between 0 and the natural height of the content. There is only a little more to it, like hiding overflow and visibility to make it look right while maintaining accessibility:
That’s wonderful. Let’s get some stars on this issue and maybe Chrome will pick it up. But of course, even better would be if auto height transitions just started working. I can’t imagine that’s totally outside the realm of possibility.
