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diff --git a/testing/web-platform/tests/css/css-contain/container-queries/container-name-tree-scoped.html b/testing/web-platform/tests/css/css-contain/container-queries/container-name-tree-scoped.html
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+++ b/testing/web-platform/tests/css/css-contain/container-queries/container-name-tree-scoped.html
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+<!doctype html>
+<meta charset="utf-8">
+<title>CSS Container Queries Test: Tree scoped container-name</title>
+<link rel="help" href="https://drafts.csswg.org/css-contain-3/#query-container">
+<link rel="help" href="https://drafts.csswg.org/css-scoping-1/#shadow-names">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/declarative-shadow-dom-polyfill.js"></script>
+<script src="support/cq-testcommon.js"></script>
+
+<div id="container-name-host">
+  <div>
+    <template shadowroot="open">
+      <style>
+        :host { container-name: foo; }
+      </style>
+      <slot></slot>
+    </template>
+    <div id="t1"></div>
+  </div>
+  <style>
+    #container-name-host > div {
+      container-type: inline-size;
+    }
+    #t1 { color: green; }
+    @container foo (width > 0px) {
+      #t1 { color: red; }
+    }
+  </style>
+</div>
+
+<div id="container-name-slotted">
+  <div>
+    <template shadowroot="open">
+      <style>
+        ::slotted(div) {
+          container-name: foo;
+        }
+      </style>
+      <slot></slot>
+    </template>
+    <div>
+      <div id="t2"></div>
+    </div>
+  </div>
+  <style>
+    #container-name-slotted > div > div {
+      container-type: inline-size;
+    }
+    #t2 { color: green; }
+    @container foo (width > 0px) {
+      #t2 { color: red; }
+    }
+  </style>
+</div>
+
+<script>
+  setup(() => {
+    assert_implements_container_queries();
+    polyfill_declarative_shadow_dom(document);
+  });
+
+  const green = "rgb(0, 128, 0)";
+
+  test(() => {
+    assert_equals(getComputedStyle(t1).color, green);
+  }, "Outer scope query should not match container-name set by :host rule in shadow tree");
+
+  test(() => {
+    assert_equals(getComputedStyle(t2).color, green);
+  }, "Outer scope query should not match container-name set by ::slotted rule in shadow tree");
+
+</script>