<style>
div {
  margin: 20px;
  font-family: Ahem;
}
span {
  text-decoration: underline;
  text-underline-offset: 10px;
  color: blue;
}
</style>
PASS if the underlines are green.
<div id=container>
<div><span>content</span></div>
<div style="writing-mode: vertical-lr"><span>content</span></div>
<div style="writing-mode: vertical-rl"><span>content</span></div>
</div>
<pre id=result></pre>
<script>
if (window.testRunner) {
  testRunner.dumpAsText();
  testRunner.waitUntilDone();
}
setTimeout(function() {
  if (window.internals)
    window.internals.startTrackingRepaints();
  for (let changeThis of container.getElementsByTagName("span"))
    changeThis.style.textDecorationColor = "green";
  if (window.internals) {
    result.innerText = window.internals.repaintRectsAsText();
    window.internals.stopTrackingRepaints();
  }
  if (window.testRunner)
    testRunner.notifyDone();
}, 10);
</script>