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diff --git a/testing/web-platform/tests/css/motion/animation/offset-anchor-composition.html b/testing/web-platform/tests/css/motion/animation/offset-anchor-composition.html
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+++ b/testing/web-platform/tests/css/motion/animation/offset-anchor-composition.html
@@ -0,0 +1,80 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>offset-anchor composition</title>
+<link rel="author" title="Eric Willigers" href="mailto:ericwilligers@chromium.org">
+<link rel="help" href="https://drafts.fxtf.org/motion-1/#offset-anchor-property">
+<meta name="assert" content="offset-anchor supports animation.">
+
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/css/support/interpolation-testcommon.js"></script>
+
+<style>
+.target {
+  width: 200px;
+  height: 200px;
+}
+</style>
+<body>
+<script>
+test_composition({
+  property: 'offset-anchor',
+  underlying: '40px 60px',
+  addFrom: '60px 40px',
+  addTo: '160px 140px',
+}, [
+  {at: -0.25, expect: '75px 75px'},
+  {at: 0, expect: '100px 100px'},
+  {at: 0.25, expect: '125px 125px'},
+  {at: 0.5, expect: '150px 150px'},
+  {at: 0.75, expect: '175px 175px'},
+  {at: 1, expect: '200px 200px'},
+  {at: 1.25, expect: '225px 225px'},
+]);
+
+test_composition({
+  property: 'offset-anchor',
+  underlying: 'top 20% left 40%',
+  addFrom: 'left 60% top 80%',
+  addTo: 'right 80% bottom 40%',
+}, [
+  {at: -0.25, expect: '110% 105%'},
+  {at: 0, expect: '100% 100%'},
+  {at: 0.25, expect: '90% 95%'},
+  {at: 0.5, expect: '80% 90%'},
+  {at: 0.75, expect: '70% 85%'},
+  {at: 1, expect: '60% 80%'},
+  {at: 1.25, expect: '50% 75%'},
+]);
+
+test_composition({
+  property: 'offset-anchor',
+  underlying: '40px 60px',
+  replaceFrom: '100px 200px',
+  addTo: '160px 40px',
+}, [
+  {at: -0.25, expect: '75px 225px'},
+  {at: 0, expect: '100px 200px'},
+  {at: 0.25, expect: '125px 175px'},
+  {at: 0.5, expect: '150px 150px'},
+  {at: 0.75, expect: '175px 125px'},
+  {at: 1, expect: '200px 100px'},
+  {at: 1.25, expect: '225px 75px'},
+]);
+
+test_composition({
+  property: 'offset-anchor',
+  underlying: '40px 60px',
+  addFrom: '60px 140px',
+  replaceTo: '200px 100px',
+}, [
+  {at: -0.25, expect: '75px 225px'},
+  {at: 0, expect: '100px 200px'},
+  {at: 0.25, expect: '125px 175px'},
+  {at: 0.5, expect: '150px 150px'},
+  {at: 0.75, expect: '175px 125px'},
+  {at: 1, expect: '200px 100px'},
+  {at: 1.25, expect: '225px 75px'},
+]);
+</script>
+</body>