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+++ b/testing/web-platform/tests/css/css-anchor-position/anchor-center-offset-change.html
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+<!DOCTYPE html>
+<title>CSS Anchor Positioning Test: Dynamically change the anchor-center position</title>
+<link rel="help" href="https://drafts.csswg.org/css-anchor-position-1/#anchor-center">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<style>
+  #cb {
+    position: relative;
+    width: 200px;
+    height: 200px;
+  }
+  #anchor {
+    width: 100px;
+    height: 100px;
+    anchor-name: --anchor;
+  }
+  #anchored {
+    position: absolute;
+    width: 100px;
+    height: 100px;
+    position-anchor: --anchor;
+    align-self: anchor-center;
+    left: anchor(--unknown right, 0px);
+  }
+</style>
+<div id="cb">
+  <div id="anchor"></div>
+  <div id="anchored"></div>
+</div>
+<script>
+  test(() => {
+    assert_equals(anchored.offsetLeft, 0);
+    assert_equals(anchored.offsetTop, 0);
+  }, "Anchored initially have the same width as the anchor");
+
+  test(() => {
+    anchor.style.height = "200px";
+    assert_equals(anchored.offsetLeft, 0);
+    assert_equals(anchored.offsetTop, 50);
+  }, "Increase the height of the anchor to move the anchor-center offset");
+</script>