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<!doctype html>
<html lang=en>
<meta charset=utf-8>
<title>CSS-contain test reference</title>
<style>
html::before {
content: "";
width: 100px;
height: 100px;
background: orange;
display: block;
}
body { margin: 0; }
p {
margin: 0;
width: 200px;
height: 200px;
}
</style>
<p>Test passes if the orange square is in the upper-left corner.