<!DOCTYPE HTML>
<html>
<head>
  <title>CSS sibling-index() and sibling-count()</title>
  <link rel="help" href="https://drafts.csswg.org/css-values-5/#tree-counting" />
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
  <style>
    html {
      z-index: calc(sibling-index() * 2);
      widows: calc(sibling-count() * 2);
    }
    #test {
      z-index: calc(sibling-index());
      counter-increment: foo calc(sibling-count());
      left: calc(10% 