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chromium/third_party/blink/web_tests/fast/css/negative-nth-child.html 

<html>
<head>
<style>
div { background-color:green; height:1em }
div:nth-child(-2n+1) { background-color:red }
div:first-child { background-color:green }
</style>
</head>
<body>
There should be only green below.  If you see RED the test has failed.
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