index.html

<!doctype html>
<html lang="en">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1" />
    <title>Example</title>
    <meta name="description" content="An example site." />
  </head>
  <body>
    <main><slot></slot></main>
    <aside><slot></slot></aside>
  </body>
</html>