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<!DOCTYPE html>
<meta charset="utf-8">
<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring-1/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<html>
<head>
<style type="text/css">
#scroller {
overflow: scroll;
height: 500px;
height: 500px;
}
#before {
height: 200px;
}
#anchor {
position: relative;
width: 200px;
height: 200px;
margin-bottom: 500px;
background-color: blue;
/*
* To trigger the Gecko bug that's being regression-tested here, we
* need 'top' to start out at a non-'auto' value, so that the
* dynamic change can trigger Gecko's "RecomputePosition" fast path
*/
top: 0px;
}
</style>
</head>
<body>
<div id="scroller">
<div id="before">
</div>
<div id="anchor">
</div>
</div>
<script type="text/javascript">
test(() => {
let scroller = document.querySelector('#scroller');
let before = document.querySelector('#before');
let anchor = document.querySelector('#anchor');
// Scroll down to select #anchor as a scroll anchor
scroller.scrollTop = 200;
// Adjust the 'top' of #anchor, which should trigger a suppression
anchor.style.top = '10px';
// Expand #before and make sure we don't apply an adjustment
before.style.height = '300px';
assert_equals(scroller.scrollTop, 200);
}, 'Positioned ancestors with dynamic changes to offsets trigger scroll suppressions.');
</script>
</body>
</html>
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