chromium/third_party/blink/web_tests/fast/css/variables/read-from-computed-style.html

<!DOCTYPE html>
<script src="../../../resources/testharness.js"></script>
<script src="../../../resources/testharnessreport.js"></script>
<style>
#container {
  --a: it was the best of times;
  --b: it was the worst of times;
  --c: also the blurst of times;
}

#b {
  --c: it was the age of wisdom;
}
</style>

<div id="container">
  <div id="a"></div>
  <div id="b"><div id="c"></div></div>
</div>

<script>
test(function() {
  assert_equals(getComputedStyle(container).getPropertyValue("--a"), "it was the best of times");
  assert_equals(getComputedStyle(container).getPropertyValue("--b"), "it was the worst of times");
  assert_equals(getComputedStyle(container).getPropertyValue("--c"), "also the blurst of times");
  assert_equals(getComputedStyle(container).getPropertyValue("--d"), "");
}, 'Directly declared custom properties appear in computed style.');

test(function() {
  assert_equals(getComputedStyle(a).getPropertyValue("--a"), "it was the best of times");
  assert_equals(getComputedStyle(a).getPropertyValue("--b"), "it was the worst of times");
  assert_equals(getComputedStyle(a).getPropertyValue("--c"), "also the blurst of times");
  assert_equals(getComputedStyle(a).getPropertyValue("--d"), "");
}, 'Inherited custom properties appear in computed style.');

test(function() {
  assert_equals(getComputedStyle(b).getPropertyValue("--a"), "it was the best of times");
  assert_equals(getComputedStyle(b).getPropertyValue("--b"), "it was the worst of times");
  assert_equals(getComputedStyle(b).getPropertyValue("--c"), "it was the age of wisdom");
  assert_equals(getComputedStyle(b).getPropertyValue("--d"), "");
}, 'Inherited custom properties overidden values appear correctly in computed style.');

test(function() {
  assert_equals(getComputedStyle(c).getPropertyValue("--a"), "it was the best of times");
  assert_equals(getComputedStyle(c).getPropertyValue("--b"), "it was the worst of times");
  assert_equals(getComputedStyle(c).getPropertyValue("--c"), "it was the age of wisdom");
  assert_equals(getComputedStyle(c).getPropertyValue("--d"), "");
}, 'Overidden and inherited custom properties appear in computed style.');
</script>