ASP .NET AJAX TabContainer - Underline the text in the selected tab

Question

I'm trying to underline the tab with the asp .net ajax control toolkit tabcontainer that is currently selected and set the aria-selected attribute for section 508. I have tried several different ways to do this. I am using the following code that has been setup to run on each partial postback of an update panel.

function pageLoadHandle(sender, Aargs) {
    var tabHeader = $('.ajax__tab_active');
    var allTabs = $('.ajax__tab_inner');
    for (var i = 0; i <= allTabs.length - 1; i++) {
        var tab = allTabs[i];
        tab.setAttribute("aria-selected", "false");
    }
    var tabAnchor = tabHeader.find("a[class=ajax__tab_tab]");
    //alert(tabAnchor);
    tabAnchor.attr("aria-selected", "true");
    tabAnchor.css("text-decoration", "underline");
}

The problem that I am seeing is that neither the aria-selected attribute is being set to true or the text is being underline. If you have some suggestions on how to get this working correctly, please let me know. I think the problem is that I am using the wrong query in the .find() method, but dang it, I'm confused. TIA

I'm pulling my hair out on this, so expect some stupidity here. :-)