How can I change the accordian pane's cssclass onmouseover event

Question

I have an accordion pane which has two classes one for selected header and other for non selected assigned to it. Both these classes have a background attribute which consists of an image. Both these images are different. Now I need to change the class of the accordion pane onmouseover and onmouseout events. These new classes will hav two different images. Below is my aspx change and the javascript function.

    <aic:AccordionPane
        HeaderCssClass="chevronSummaryHeader"
        HeaderSelectedCssClass="chevronSummaryHeaderSelected"
        ContentCssClass="chevronSummaryContent" runat="Server"
        id="apWhatHappened" onmouseover="mouseover(this.id)" onmouseout="mouseout(this.id)">            
        <Header>                        
           <div class="chevronSummaryHeaderText">
           <aic:label ID="lblWhatHappened" runat="server" Text="{[Allstate.Claims.NextGen.CSS.Resources].GeneralFactsCR.WhatHappenedHeader}"></aic:label></div>
           <aic:LinkButton ID="btnWhatHappened"  Text="" runat="server" CssClass="summaryEditButton" />
        </Header>
        <Content>                          
            <ql:QuestionList ID="ucWhatHappened" runat="server" EnableViewState="true" />                                
        </Content>        
    </aic:AccordionPane> 

function cancelBubble(e) { if(e.stopPropagation) e.stopPropagation(); e.cancelBubble = true; }

function mouseover(id) 
{ 
    if(id.className == "chevronSummaryHeader")
    {
        id.setAttribute("class", "chevronMouseOverSummaryHeader");
    }
    else if (id.className =="chevronSummaryHeaderSelected")
    {
        id.setAttribute("class", "chevronMouseOverSummaryHeaderSelected");
    }
} 

function mouseout(id) 
{            
    if(id.className =="chevronMouseOverSummaryHeader")
    {
        id.setAttribute("class", "chevronSummaryHeader");
    }
    else if (id.className =="chevronMouseOverSummaryHeaderSelected")
    {
        id.setAttribute("class", "chevronSummaryHeaderSelected");
    }
}

Now when I hover the mouse there is no change in the class of accordion pane. I am not getting what is going wrong.