chromium/third_party/blink/web_tests/fast/css-grid-layout/containing-block-grids.html

<!DOCTYPE html>
<html>
<head>
    <link href="resources/grid.css" rel="stylesheet">
    <style>
        div { width: 100px; height: 100px; }
        .relative-positioned-grid { background-color: red; position:relative; }
        .relative-positioned-inline-grid { background-color: red; position: relative; }
    </style>
</head>
<body>
<p>Grids can act as containing blocks for positioned content.</p>
<div class="relative-positioned-grid grid"><div style="background-color: green; left: 0; top: 0"></div></div>
<div class="relative-positioned-inline-grid inline-grid"><div style="background-color:green; left: 0; top: 0"></div></div>
</body>
</html>