css/css-grid/grid-with-content-dynamic-display-001.html

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1740702">
<link rel="match" href="../reference/ref-filled-green-100px-square-only.html">
<style>
  #grid {
    display: grid;
    width: 100px;
    height: 100px;
    background: red;
  }

  #initiallyHidden {
    display: none;
    width: 100px;
    height: 100px;
    background: green;
  }
</style>
</head>
<body>
  <p>Test passes if there is a filled green square.</p>
  <div id="grid">
    <div>
      <div>
        <div>
          <div id="initiallyHidden">
          </div>
        </div>
      </div>
    </div>
  </div>
  <script>
  "use strict";

  const grid = document.getElementById("grid");
  const initiallyHidden = document.getElementById("initiallyHidden");
  document.documentElement.offsetHeight; // Flush layout

  // Fails in buggy Firefox build because it prevents reflows from happening
  getComputedStyle(grid).getPropertyValue("grid-template-columns");

  document.documentElement.offsetHeight; // Flush layout again

  initiallyHidden.style.display = "block"; // This should trigger a reflow.
  </script>
</body>
</html>