chromium/third_party/blink/web_tests/external/wpt/html/rendering/the-details-element/details-pseudo-elements-003-ref.html

<!DOCTYPE HTML>
<title>::details-content pseudo element is display: block</title>
<style>

#contents { opacity: 0.5; }

details

</style>

<div>
  <div>summary</div>
  <div id="contents">contents</div>
</div>