<!DOCTYPE html>
<html>
<body style="font-family: ahem; -webkit-font-smoothing: none;">
<style>
    div.table { display: table; }
    div.section { display: table-row-group; }
    div.test { background-color: green; width: 50px; height: 50px; }
</style>

<div class="table" id="table-1">
    <div class="section" id="tbody-1">
    </div>
    <div class="section" id="tbody-2">
    </div>
</div>

<script>
    function createDiv()
    {
      var divElement = document.createElement("div");
      divElement.setAttribute("class", "test");
      return divElement;
    }

    function insertDiv(tableID, beforeID)
    {
        var table = document.getElementById(tableID);
        var before = document.getElementById(beforeID);
        table.insertBefore(createDiv(), before);
    }

    document.body.offsetTop;

    insertDiv("table-1", "tbody-2");
</script>
</body>
</html>