chromium/third_party/blink/web_tests/fast/block/positioning/fixed-position-stacking-context2.html

<!DOCTYPE html>
<title>Fixed position elements do establish stacking contexts with setting enabled</title>
<style>
div {
    height: 100px;
    width: 100px;
    margin: 0;
    padding: 0;
    top: 0;
    left: 0;
    position:fixed;
}

.green {
    position:fixed;
    background: green;
    z-index: 1;
}

.red {
    position:fixed;
    background: red;
    z-index: 2;
}
</style>
<div class="green"></div>
<div class="container">
  <div class="green"></div>
  <div class="red"></div>
</div>