css/cssom/StyleSheetList-constructable.html

<!DOCTYPE html>
<html>
  <head>
    <title>CSSOM - StyleSheetList does not include adopted style sheets</title>
    <link rel="help" href="https://drafts.csswg.org/cssom/#css-style-sheet-collections">
    <script src="/resources/testharness.js"></script>
    <script src="/resources/testharnessreport.js"></script>
    <style id="sheet1">
      body { width: 50%; }
    </style>
  </head>
  <body>
    <script>
      test(() => {
        const sheet = new CSSStyleSheet();
        document.adoptedStyleSheets = [sheet];

        var styleSheets = document.styleSheets;
        assert_equals(styleSheets.length, 1);
        assert_equals(styleSheets[0], sheet1.sheet);
      }, 'document.styleSheets does not include adopted style sheets');
    </script>
  </body>
</html>