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Thanks for the pull request. I would think that the filter method filerStyleAndLinkAttributesInDocumentFragment would catch the inline style tag and filter it out of the loop, thus never getting into this problem. A simple example shows that this is what happens. Do you know why in your case the filter is letting the inline style tag through?

<div id="shadow"></div>
<script>
    const root = shadow.attachShadow({ mode: 'open' });
    root.innerHTML = `
      <!-- this is filtered out of the getStylesheetsFromDocumentFragment loop -->
      <style>
      a { color: red }
      </style>
      <a href="#">hello world</a>
  `;
</script>

@EduSantosBrito Quick ping, have you had a chance to look at Steve's comment?

Hey! I have time this week to look at it. I was on holiday last week hahaha

Ok, after debugging for some hours I found that document.implementation.createHTMLDocument breaks HTMLStyleElement.sheet. There's some issues opened related to that jsdom/jsdom#3179

This makes sense why the browser using selenium-webdriver was working and the test using jsdom wasn't.

Quick ping @WilcoFiers @straker

That makes sense. Thanks for the looking into that for us.

Approved for security.