top-layer-containing-block-ref.html

<!DOCTYPE html>
<html>
<head>
<link rel="stylesheet" href="resources/dialog.css">
</head>
<body>
<p>
This tests that a modal dialog's containing block is in the initial containing block and that it is unaffected by
ancestor elements with overflow or opacity.
<div class="pseudodialog" style="position: absolute; top: 100px; height: 250px; width: 90%; background-color: yellow">
    This dialog should be onscreen with a width of 90% of the page. It is the child of an narrow element
    positioned off screen, but the containing block of a top layer element is the initial containing block, so its
    position and percent lengths are relative to that.
</div>
<div class="pseudodialog" style="position: absolute; top: 200px; left: 0px; height: 100px; background-color: cyan">
    This dialog should be unaffected by its ancestor with overflow. It should not be clipped.
</div>
<div class="pseudodialog" style="position: absolute; top: 250px; left: 0px; background-color: magenta">
    This dialog should be unaffected by its ancestor with opacity.
</div>
</body>
</html>

chromium/third_party/blink/web_tests/external/wpt/html/semantics/interactive-elements/the-dialog-element/top-layer-containing-block-ref.html