<!doctype html>
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<html><head>
  <meta charset="utf-8">
  <title>Reference: content:none on a :root flex</title>
  <link rel="author" title="Mats Palmgren" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1699964">
  <style>
html,body {
  padding:0; margin:0;
}
body {
  display: flex;
  border: 1px solid;
  gap: 10px;
}
  </style>
</head>
<body><x>B</x><x>A</x></body>
</html>