<!DOCTYPE html>
<link rel="help" href="https://html.spec.whatwg.org/C/#the-fieldset-and-legend-elements">
<!-- A test for the following paragraph:
The element is expected to be positioned in the block-flow direction such that
its border box is centered over the border on the block-start side of the
fieldset element.
-->
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style>
fieldset {
  margin: 0;
  padding: 0;
  border: 100px solid black;
}
legend {
  height: 0px;
  border-color: yellow;
  border-style: solid;
}
</style>
<fieldset>
<legend style="border-width:50px"></legend>
<br>
</fieldset>
<br>

<fieldset>
<legend style="border-width:25px 50px"></legend>
<br>
</fieldset>
<br>

<fieldset>
<legend style="border-width:10px 50px 40px 50px"></legend>
<br>
</fieldset>
<br>

<fieldset>
<legend style="border-width:40px 50px 10px 50px"></legend>
<br>
</fieldset>

<script>
function legendBlockOffset(fieldset) {
  let legend = fieldset.querySelector('legend');
  return legend.getBoundingClientRect().y - fieldset.getBoundingClientRect().y;
}

test(() => {
  let fieldsets = document.querySelectorAll('fieldset');
  assert_equals(legendBlockOffset(fieldsets[0]), 0);
  assert_equals(legendBlockOffset(fieldsets[1]), 25);
  assert_equals(legendBlockOffset(fieldsets[2]), 25);
  assert_equals(legendBlockOffset(fieldsets[3]), 25);
}, 'Legend\'s border-box should be centere on the fieldset border');
</script>
