<!DOCTYPE html>
<html class="reftest-wait">
<style>
html, body {
    margin: 0;
}
thead tr {
    position: relative;
    top: 50px;
}
th {
    background-color: green;
    height: 20px;
}
td {
    background-color: blue;
}
</style>
<body>
<table cellspacing=0>
    <thead>
        <tr><th></th></tr>
    </thead>
    <tbody>
        <tr><td style="height: 2000px; vertical-align: top">table cell</td></tr>
    </tbody>
</table>
<script>
  addEventListener('load', function() {
    document.scrollingElement.scrollTop = 50;
    document.documentElement.classList.remove('reftest-wait');
  }, false);
</script>
</html>