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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>
<style>
#scroller {
overflow: scroll;
width: 300px;
height: 300px;
}
#before { height: 50px; }
#content { margin-top: 100px; margin-bottom: 600px; }
.no { overflow-anchor: none; }
</style>
<div id="scroller">
<div id="before"></div>
<div id="content">content</div>
</div>
<script>
// Tests that dynamic styling 'overflow-anchor' on a scrolling element has the
// same effect as initial styling
test(() => {
let scroller = document.querySelector("#scroller");
let before = document.querySelector("#before");
// Scroll down so that #content is the first element in the viewport
scroller.scrollTop = 100;
// Change the height of #before to trigger a scroll adjustment. This ensures
// that #content was selected as a scroll anchor
before.style.height = "100px";
assert_equals(scroller.scrollTop, 150);
// Now set 'overflow-anchor: none' on #scroller. This should invalidate the
// scroll anchor, and #scroller shouldn't be able to select an anchor anymore
scroller.className = 'no';
// Change the height of #before and make sure we don't adjust. This ensures
// that #content is not a scroll anchor
before.style.height = "150px";
assert_equals(scroller.scrollTop, 150);
}, "Dynamically styling 'overflow-anchor: none' on the scroller element should prevent scroll anchoring");
</script>
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