css/CSS2/abspos/hypothetical-box-dynamic.html

<!doctype html>
<html class="reftest-wait">
<title>Layout is correctly updated when the hypothetical display of an element changes, even though the final computed display doesn't</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://drafts.csswg.org/css2/visudet.html#abs-non-replaced-height" title="10.6.4 Absolutely positioned, non-replaced elements">
<link rel="match" href="hypothetical-box-dynamic-ref.html">
<style>
  div {
    font: 16px / 1 monospace;
    text-align: center;
    margin: 5px;
    position: relative;
    min-height: 30px;
  }
  span {
    position: absolute;
  }
  .block {
    display: block;
  }
</style>
<p>Should see two words at the same horizontal position below:</p>
<div>
  <span class="block">Foo</span>
</div>
<div>
  <span>Foo</span>
</div>
<script>
onload = function() {
  requestAnimationFrame(() => requestAnimationFrame(() => {
    document.querySelector(".block").className = "";
    document.documentElement.className = "";
  }));
}
</script>