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chromium/third_party/blink/web_tests/fast/forms/select/select-item-background-clip.html 

<html>
<head>
    <title></title>
</head>
<body>
    <p>
        Test for <i><a href="http://bugs.webkit.org/show_bug.cgi?id=12364">http://bugs.webkit.org/show_bug.cgi?id=12364</a>
        REGRESSSION (NativeListBox): Selected option's background is not clipped to the list box</i>.
    </p>
    <select size="4" style="border: 3px solid blue; padding: 3px;" id="sel">
        <option>one</option>
        <option>two</option>
        <option>three</option>
        <option style="background-color: purple;">four</option>
    </select>
<script>
var sel = document.getElementById('sel');
var itemHeight = (sel.offsetHeight - 11) / sel.size;
sel.style.height = (11 + itemHeight * 3 + 5) + 'px';
</script></body>
</html>