appmanifest/display-member/display-member-media-feature-fullscreen-manual.html

<!DOCTYPE html>
<title>Test "fullscreen" value of display member + media feature</title>
<link rel="help" href="https://w3c.github.io/manifest#display-member" />
<link rel="help" href="https://w3c.github.io/manifest/#dom-displaymodetype-fullscreen" />
<link rel="help" href="https://w3c.github.io/manifest/#the-display-mode-media-feature" />
<link rel="manifest" href="display-member-media-feature-fullscreen.webmanifest" />
<meta name="viewport" content="width=device-width, initial-scale=1">
<h1>Testing support for "fullscreen" value of display member + media feature</h1>
<style>
  .fail {
    background-color: red;
  }

  @media all and (display-mode: fullscreen) {
    body {
      background-color: green;
    }
  }
</style>
<script>
const fullscreen = matchMedia("(display-mode: fullscreen)");

fullscreen.onchange = () => {
  if (fullscreen.matches) {
    document.body.classList.remove("fail");
  }
}

if (!fullscreen.matches) {
  document.body.classList.add("fail");
}
</script>
<p>
  To pass, the background color must be green after installing.
</p>