css/css-nesting/invalidation-002.html

<!doctype html>
<title>CSS Selectors nested invalidation on changed child</title>
<link rel="author" title="Steinar H. Gunderson" href="mailto:sesse@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-nesting-1/">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
  .a {
    color: green;
  }
  .a {
    & .b {
      color: red;
    }
  }
</style>

<div id="container" class="a">
  <div id="child" class="b">
    Test passes if color is green.
  </div>
</div>

<script>
  test(() => {
    let container = document.getElementById('container');
    let child = document.getElementById('child');
    assert_equals(getComputedStyle(child).color, 'rgb(255, 0, 0)');
    child.classList.remove('b');
    assert_equals(getComputedStyle(child).color, 'rgb(0, 128, 0)');
  });
</script>