style-contain-dialogue-element.html

<!DOCTYPE html>
<style>
.contain { contain: style; }
.reset { counter-reset: c;}
.increment::before { content: counters(c, "."); }
.increment { counter-increment: c; }
</style>
<div class="increment"></div>
<div class="contain">
    <dialog id="test">
        <div class="increment"></div>
    </dialog>
</div>
<div class="increment"></div>
<script>
document.getElementById("test").showModal();
</script>

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