test_document_adopted_styles.html

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<!doctype html>

<meta charset="utf-8">

<div class="target"></div>

<script>

  const sheet = new CSSStyleSheet();

  document.adoptedStyleSheets = [sheet];

  sheet.replaceSync(".target { width: 100px; height: 100px; border-style: solid; border-color: blue; }");

</script>