css3 scale transform on parent div but keeping con

Question

I'm using css3 scale transform to scale a div that contains other divs inside.

The problem I have is that some of the inner divs I need to keep as they were, basically as if they were not scaled, their size should not change, however I do need to scale the parent div with everything else inside.

How can you reverse the scaling in some of the divs?
I am trying to apply an inverse scaling.
If the overall div had applied a value of 1.5 , I'm trying to find what value I should now scale the other divs to revert them visually to how they looked before.

Answer 1

The inverse of any scale operation is 1 / <scale> so by scaling the container by 1.5 you would need to scale the children by 1 / 1.5 = 0.6

Unfortunately, according to the specification you cannot just use CSS like:

transform: scale(1/1.5);

since scale is defined as scale(<number>[, <number>])

where <number> is

either an or zero or more decimal digits followed by a dot (.) followed by one or more decimal digits

So you'll have to do the calculation yourself or could use a dynamic stylesheet language like LESS which supports these sort of operations.

Demo (webkit only)

Answer 2

If the parent div has been scaled by a factor of 1.5, then you need to scale the children by a factor of 1/1.5 = 0.(6) to keep their size constant.

example

In general, in order to cancel for a child element a scale transform that has been applied on the parent and has a scale factor of a, you need to apply another scale transform of factor 1/a on the child itself.

You either need to:

• compute manually the scale factor before you do anything else and then use it as it is in your code (example linked above)
• use a preprocessor to handle this for you (SASS example)
• use JavaScript to compute the scale factor needed for the child and to set the scale transform on the child

Answer 3

If you, as suggested, use the inverted the scale factor, then note that the child does not necessarily keep its original size during the scale transformation -- this matters of course only if you let the scale transforms have a duration (e.g. by using transition: transform;).

Answer 4

You could use a CSS variable to store your scale factor, and then use calc() to calculate the inverse scale for the child elements that have a certain class:

.wrapper {
  transform: scale(var(--scale));
  background: #ffffd;
}

.wrapper > * {
  text-align: center;
}

.wrapper > .revertscale {
  transform: scale(calc(1/var(--scale)));
}

<div class="wrapper" style="--scale: 0.8">
  <h2>scaled title</h2>
  <p>scaled description</p>
</div>

<div class="wrapper" style="--scale: 0.8">
  <h2 class="revertscale">not scaled title</h2>
  <p class="revertscale">not scaled description</p>
</div>

⋅ ⋅ ⋅

In case you don't want any of the child elements to scale, another way of doing it would be to style your wrapper as a pseudo element :

.wrapper {
  position: relative;
}

.wrapper > * {
  text-align: center;
}

.wrapper::before {
  content: "";
  z-index: -1;
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  transform: scale(var(--scale));
  background: #ffffd;
}

<div class="wrapper" style="--scale: 1">
  <h2>title</h2>
  <p>description</p>
</div>

<div class="wrapper" style="--scale: 1.2">
  <h2>title</h2>
  <p>description</p>
</div>

<div class="wrapper" style="--scale: 0.8">
  <h2>title</h2>
  <p>description</p>
</div>