css/css-values/calc-sibling-function.html

<!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>
    #test {
      z-index: calc(sibling-index());
      counter-increment: foo calc(sibling-count());
      left: calc(10% + 100px * sibling-index());
    }
    #test::before {
      z-index: calc(sibling-index() * 2);
    }
  </style>
</head>
<body>
  <div>
    <div></div>
    <div id="test"></div>
    <div></div>
    <div></div>
    <ul></ul>
  </div>
  <script>
test(() => {
  let style = getComputedStyle(document.getElementById('test'));
  assert_equals(style.zIndex, '2');
}, 'basic sibling-index() test');

test(() => {
  let style = getComputedStyle(document.getElementById('test'));
  assert_equals(style.counterIncrement, 'foo 5');
}, 'basic sibling-count() test');

test(() => {
  let style = getComputedStyle(document.getElementById('test'));
  assert_equals(style.left, 'calc(10% + 200px)');
}, 'sibling-index() in calc() with percentage');

test(() => {
  let style = getComputedStyle(document.getElementById('test'), ':before');
  assert_equals(style.zIndex, '4');
}, 'sibling-count on pseudo-element');
  </script>
</body>
</html>