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<!DOCTYPE html>
<title>CSS Anchor Positioning: Transition when position-anchor changes</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/">
<link rel="help" href="https://github.com/w3c/csswg-drafts/issues/9598">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
#cb {
display: inline-block;
position: relative;
width: 250px;
height: 250px;
border: 1px solid black;
}
#anchor1, #anchor2 {
width: 100px;
}
#anchor1 {
background: wheat;
height: 50px;
anchor-name: --a1;
}
#anchor2 {
background: tomato;
height: 90px;
anchor-name: --a2;
}
#anchored {
position: absolute;
width: anchor-size(width);
height: anchor-size(height);
top: anchor(top);
left: anchor(right);
transition-duration: 1000s;
transition-timing-function: steps(2, start);
transition-property: top, height;
background-color: skyblue;
position-anchor: --a1;
}
</style>
<div id=cb>
<div id=anchor1>Anchor1</div>
<div id=anchor2>Anchor2</div>
<div id=anchored></div>
</div>
<script>
test(() => {
assert_equals(anchored.offsetTop, 0);
assert_equals(anchored.offsetHeight, 50);
anchored.style.positionAnchor = '--a2';
assert_equals(anchored.offsetTop, 25);
assert_equals(anchored.offsetHeight, 70);
}, 'Transition when position-anchor changes');
</script>
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