color: white;
}
.hidden {
  content-visibility: hidden;
}
</style>

<div>Test passes if the word “PASS” and a green box can been seen below.</div>
<iframe id="frame" class=hidden width=400 height=200 srcdoc='
  <style>
  div {
    background: green;
  }
  </style>
  <div>PASS</div>
'></iframe>
<div>Lorem ipsum consectetur adipiscing elit</div>

<script>
async function runTest() {
  document.getElementById("frame").classList.remove("hidden");
  requestAnimationFrame(takeScreenshot);
}

window.onload = ()