css/cssom/cssstyledeclaration-nested.html

<!DOCTYPE html>
<title>CSSNestedDeclarationBlock cssom interactions</title>
<link rel="help" href="https://drafts.csswg.org/css-nesting/#the-cssnestrule">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<style id="s1">
.parent {
  color: red;
  .child { background: blue; }
  font-size: 20px;
}
</style>
<div class="parent"><div class="child">C</div></div>
<script>
test(function() {
  const sheet = document.getElementById('s1').sheet;
  const nested = sheet.cssRules[0].cssRules[1];
  assert_true(nested instanceof CSSNestedDeclarations, "Should be a nested declarations rule");
  nested.style.color = "green";
  assert_equals(
    getComputedStyle(document.querySelector(".parent")).color,
    "rgb(0, 128, 0)",
    "Parent should be green now"
  );
});
</script>