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<!doctype html>
<html>
<head>
<link rel="help" href="https://www.w3.org/TR/css-position-3/#def-cb">
<link rel="help" href="https://crbug.com/970171">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#container {
position: relative;
border: 1px solid black;
}
.narrow {
width: 200px;
height: 300px;
}
.wide {
width: 300px;
height: 200px;
}
#target {
background: green;
position: absolute;
width: 50px;
height: 30px;
left: 50%;
top: 50%;
margin-left: -25px;
margin-top: -15px;
}
</style>
</head>
<body>
<div id="container" class="narrow">
<button id="target"></button>
</div>
<script>
test( t => {
let container = document.querySelector("#container");
let target = document.querySelector("#target");
document.body.offsetTop;
// start off narrow
let narrow_left = target.offsetLeft;
let narrow_top = target.offsetTop;
// make it wide
container.classList.toggle("narrow");
container.classList.toggle("wide");
document.body.offsetTop;
// make it narrow again
container.classList.toggle("narrow");
container.classList.toggle("wide");
document.body.offsetTop;
assert_equals(target.offsetLeft, narrow_left);
assert_equals(target.offsetTop, narrow_top);
}, "absolute positioned button with percentage top gets positioned");
</script>
</body>
</html>
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