sousa-gecko/testing/web-platform/tests/css/css-images/linear-gradient-sibling-index.html

<!DOCTYPE html>
<title>CSS Images Test: Linear gradient with sibling-index()</title>
<link rel="help" href="https://drafts.csswg.org/css-images/#linear-gradients">
<link rel="help" href="https://drafts.csswg.org/css-values-5/#tree-counting">
<link rel="match" href="linear-gradient-sibling-index-ref.html">
<style>
  .grad {
    width: 100px;
    height: 100px;
    background: linear-gradient(blue calc(10px * sibling-index()), yellow);
  }
</style>
<div>
  <div></div>
  <div class="grad"></div>
  <div></div>
  <div></div>
  <div class="grad"></div>
</div>