how to retain fixed positions of elements inside transformed elements?

Question

it's a known 'bug' that elements with fixed position loose their position if the container is translated. For example, if i've got a structure like this:

<div class="container">
   <div class="fixed"></div>
</div>

and, say, the container is scrolled, when the conteiner gets transformed (say, translate(x,y), rotate(), or so..), then the fixed element behaves like it was positioned relative and it scrolls with the container. I can see it on the latest firefox, for example.

How can one fix this kind of problem? Is there any way?

Answer 1

This behaviour is not a bug. It's actually the specs recommended behaviour.
(See this post by Eric Meyer, or this question here on SO which accepted solution only provides a link to the same meyer's post)

For those who don't know this issue, and because you didn't provide a snippet into your question, here's one.

document.addEventListener('click', function() {
  document.getElementById('container').classList.toggle('transformed')
}, false);

#bg {
  border: 1px solid #AFA;
  height: 100%;
  width: 100%;
  position: fixed;
  top: 0;
  left: 0;
}
#container {
  border: 1px solid #FAF;
  height: 50%;
  width: 75%;
  position: relative;
  margin: 0 auto;
  overflow: auto;
}
#content {
  background: rgba(125, 175, 0, .7);
  position: fixed;
  width: 100%;
  top: 0;
  left: 0;
}
.transformed {
  transform: translate(0, 5em);
}

<div id="bg">
  <div id="container" class="transformed">
    .<br>.<br>.<br>.<br>.<br>.<br>.
    this is a scrollable paragraph
    <br>.<br>the "fixed" content does scroll with the paragraph
    <br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.
    you can click to toggle the transformation On/Off
    <br>.<br>.<br>.<br>.<br>.
    <span id="content">relatively fixed content</span>
  </div>
</div>

However, I did find something that may help others facing the same issue.
It's not really a solution, since the "fixed" element will be only inside the container, (except for IE browsers where it will really be fixed to the document). But in my case, it's actually what I wanted and maybe it'll be fine for others too.

If you add a wrapper, set its height:100%; width:100%; and overflow:auto, then your "fixed" content won't scroll with the container.

Actually it's not you container which scrolls anymore, but the wrapper. So you might want to set the container's overflow:visible or hidden to avoid unwanted scrolling of the not so well "fixed" element.
Also, note that you need your wrapper be a block or inline-block element.

#bg {
  border: 1px solid #AFA;
  height: 100%;
  width: 100%;
  position: fixed;
  top: 0;
  left: 0;
}
#container {
  border: 1px solid #FAF;
  height: 50%;
  width: 75%;
  position: relative;
  margin: 0 auto;
  overflow: visible;
}
#wrapper {
  height: 100%;
  width: 100%;
  overflow: auto;
}
#content {
  background: rgba(125, 175, 0, .7);
  position: fixed;
  width: 100%;
  top: 0;
  left: 0;
}
.transformed {
  transform: translate(0, 50%);
}

<div id="bg">
  <div id="container" class="transformed">
    <div id="wrapper">
      .<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.<br>.
      <span id="content">relatively fixed content</span>
    </div>
  </div>
</div>