Can divs below a css transform move along with divs above? - css

Question

I am using css transitions to lay out a bunch of divs on top of each other. At any point, one of the divs may collapse. And all of the divs below it are supposed to move up to fill its spot.
Here is a codepen that describes the situation.
The css I am using is the following:
div {
height: 100px;
width: 100px;
margin: 15px;
}
.top {
background-color: red;
transform-origin: top;
animation: move 2s infinite;
}
.bottom {
background-color: blue;
}
#keyframes move {
0% {
transform: rotateX(0deg);
}
50% {
transform: rotateX(90deg);
}
}
With this, the top div will expand and contract. I want the divs below it to move up as the top one collapses.
If I switch transform for height, like this:
#keyframes move {
0% {
height 0;
}
50% {
height: 100px;
}
}
The bottom divs do move, but this is not a good solution for me because in the actual application, each div has a dynamically calculated size.
How can the bottom divs move smoothly with the top div?

Answer 1

With transform you won't be able to do that, as when an element is transformed, the surrounding elements won't see any change in the DOM, as DOM-wise nothing have happened.
What you can do to optimize it all, is to prepare the browser that the height will change, with the property will-change: height
MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/will-change
This new CSS property aim's to do what transform does, make smoother and more optimized animations.
Do note though:
will-change is intended to be used as a last resort, in
order to try to deal with existing performance problems. It should not
be used to anticipate performance problems.
Another possible solution (read hack), is to trick the browser to use GPU instead of CPU, shown in this answer (see its p.1):
CSS `will-change` - how to use it, how it works
Updated
In case of the height is auto, or similar, this will work with the max-height trick, and here is a couple of answers of mine, showing how-to:
CSS Animation on max-height change
Can't use the same animation in reverse for class toggle
CSS transition auto width
And the last resort, if none of the above is applicable, is to use a small script and either create a styles dynamically (links below), or set them inline.
Dynamically styling pseudo-elements using jQuery or Javascript
How to prevent css from getting converted to inline css