page.html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <meta name="color-scheme" content="light dark" />
    <title>An element in the page</title>
    <meta property="og:title" content="An element in the page" />
    <meta property="og:type" content="website" />
    <meta name="twitter:card" content="summary" />
    <style>
      /* Pagez's theme.css */
    </style>
    <style>
      call-out {
        display: block;
        border-left: 4px solid;
        padding-left: 1rem;
      }
    </style>
  </head>
  <body>
    <main>
<h1 id="notes">Notes</h1>
<call-out type="note"><aside class="note"><p>Markdown <strong>inside</strong>, in the slot.</p>
</aside></call-out>
<call-out type="warning"><aside class="warning"><p>A second one. Its CSS is still written once.</p>
</aside></call-out>
</main>
  </body>
</html>