css/css-tables/collapsed-border-partial-invalidation-002.html

<!DOCTYPE html>
<html class="reftest-wait">
<link rel="author" title="David Shin" href="dshin@mozilla.com">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1879731">
<link rel="match" href="collapsed-border-partial-invalidation-002-ref.html">
<meta name="assert" content="Invalidating part of a border-collapsed table keeps border styling correctly.">
<style>
table {
  border-collapse: collapse;
}

.group {
  border-top: 1px solid black;
  border-bottom: 3px solid black;
}
</style>
<table id="table">
  <tr id="row"><td class="group">X</td><td>X</td><td id="last" class="group">X</td></tr>
</table>
<script>
onload = function () {
  // Make sure the table layout is flushed
  table.getBoundingClientRect();
  let td = document.createElement('td');
  td.innerText = "X";
  // Requring #last is an unfortunate side effect of bug 1880560.
  last.before(td);
  document.documentElement.className = "";
}
</script>
</html>