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chromium/third_party/blink/web_tests/external/wpt/css/css-backgrounds/fieldset-inset-shadow-ref.html 

<!doctype html>
<title>CSS Test Reference</title>
<style>
  div {
    width: 100px;
    height: 100px;
    box-sizing: border-box;
    box-shadow: 0 0 0 10px inset black;
  }
</style>
<div></div>