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<!DOCTYPE html>
<meta charset="utf-8">
<title>CSS transforms: Creating containing block for fixed positioned elements</title>
<link rel="author" title="L. David Baron" href="https://dbaron.org/">
<link rel="author" title="Mozilla" href="http://www.mozilla.org/">
<link rel="match" href="containing-block-dynamic-1-ref.html">
<meta name="assert" content="It also establishes a containing block (somewhat similar to position: relative), just like the transform property does.">
<meta name="flags" content="dom">
<style>
html, body { margin: 0; padding: 0 }
#changeperspective {
position: absolute;
top: 100px;
left: 100px;
}
#abscovered {
position: absolute;
top: 50px;
left: 50px;
background: red;
height: 100px;
width: 100px;
}
#fixedmoves {
position: fixed;
top: 50px;
left: 50px;
background: green;
height: 100px;
width: 100px;
}
</style>
<body>
<div id="changeperspective">
<div id="abscovered"></div>
<div id="fixedmoves"></div>
</div>
<script>
var changeperspective = document.getElementById("changeperspective");
var fixedmoves = document.getElementById("fixedmoves");
var causeFlush = fixedmoves.offsetTop;
changeperspective.style.perspective = "1000px";
</script>
</body>