CSS and Ajaxa Accordion

[IT_Techno]

hi
i have problem with css and accordion when i change the color of accordion head at css the accordion become very slow when close and open it i do not know what is the problem this is the part of css code that belong to accordion header

.accordionHeader
{
    border: 1px solid #2F4F4F;
    color: #d2b48c;
    background-color: #50a3be;
    font-family: Arial, Sans-Serif;
    font-size: 14px;
    font-weight: bold;
    padding: 5px;
    margin-top: 5px;
    cursor: pointer;
    vertical-align: middle;
    text-align: center;
    background-image: url(images/edge2.gif);
}

.accordionContent
{
    background-color: #fafafa;
    border: 1px dashed #2F4F4F;
    border-top: none;
    padding: 5px;
    padding-top: 10px;
}

.accordionLink
{
    vertical-align: middle;
    text-align: center;
}

AND THIS PART FROM ASPX FILE :

            <td align="right" valign="middle" width="100%" colspan="4">
               <cc1:Accordion ID="Accordion1" runat="server" SelectedIndex="0"  
                       HeaderCssClass="accordionHeader" 
                       ContentCssClass="accordionContent" 
                       FadeTransitions="false" 
                       FramesPerSecond="40" 
                       TransitionDuration="150"
                       AutoSize="None"
                       Width = "100%">

plz any one can helpe

Best Regards