var contentDivHt = document.getElementById("contentDiv").offsetHeight;
    var leftcolHt = document.getElementById("leftcol").offsetHeight;
    if (contentDivHt >= leftcolHt)
        document.getElementById('sidenav').style.height = contentDivHt + "px";
    else 
        document.getElementById('sidenav').style.height = leftcolHt + "px";