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diff --git a/testing/web-platform/tests/css/css-contain/container-queries/animation-nested-transition.html b/testing/web-platform/tests/css/css-contain/container-queries/animation-nested-transition.html
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+++ b/testing/web-platform/tests/css/css-contain/container-queries/animation-nested-transition.html
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+<!doctype html>
+<title>Container Queries - Animated container with inner transition</title>
+<link rel="help" href="https://drafts.csswg.org/css-contain-3/#animated-containers">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="support/cq-testcommon.js"></script>
+<style>
+  @keyframes outer {
+    from { width: 100px; }
+    to { width: 300px; }
+  }
+  #container {
+    container-type: inline-size;
+    animation: outer 1s linear paused;
+  }
+  #target {
+    background-color: rgb(100, 100, 100);
+  }
+
+  @container (min-width: 200px) {
+    #target {
+      transition: background-color 100s steps(2, start);
+      background-color: rgb(200, 200, 200);
+    }
+  }
+</style>
+<div id=container>
+  <div id=target>
+    Test
+  </div>
+</div>
+<script>
+  setup(() => assert_implements_container_queries());
+
+  test(() => {
+    assert_equals(getComputedStyle(target).backgroundColor, 'rgb(100, 100, 100)');
+
+    assert_equals(container.getAnimations().length, 1);
+    let animation = container.getAnimations()[0];
+    animation.currentTime = 600;
+
+    assert_equals(getComputedStyle(target).backgroundColor, 'rgb(150, 150, 150)');
+  }, 'Animated container size triggers transition');
+</script>