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chromium/third_party/blink/web_tests/fast/css/containment/style-contain-dialogue-element-expected.html 

<!DOCTYPE html>
<div>1</div>
<div>
    <dialog id="test">
        <div>1.1</div>
    </dialog>
</div>
<div>2</div>
<script>
document.getElementById("test").showModal();
</script>