Facing problem with Menu in asp.net style sheet

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ASP.NET

CSS

style

Dear Friends,

Am facing problem with Menu.

I have created a website in asp.net c# and used Css , style sheets.

my requirement is, when i select particular page from menu..MOUSE OVER Should stay on that particular page. so that user can understand that he is on this page.

This is my style sheet css

.green #slatenav
{position:relative;
 display:block;
 height:42px;
 font-size:12px;
 font-weight:bold;
 width:50%;
 background-color:#EFCC00;
font-family:Arial,Verdana,Helvitica,sans-serif;
top:0px;
left: 520px;
width:570px;
}

.green #slatenav ul{margin:0px;padding:0;list-style-type:none;width:auto; }
.green #slatenav ul li{display:block;float:left;margin:0 1px 10px 8px;}
.green #slatenav ul li a{display:block;float:left;color:#197E46;text-decoration:none;padding:14px 10px 0 10px;height:28px;
                       
 -moz-border-radius:20px;}

.green #slatenav ul li a:hover,.green #slatenav ul li a.current
{color:#fff;background:transparent url(images/greenslate_backgroundOVER.gif) no-repeat top center;}

This is my master page.
=========================

<div>

   <div class="green">
   <div id="slatenav">
   <ul>
    <li><a href="Home.aspx" onclick="Home_Click"><span>Home</span></a></li>


                 <li><a href="AboutUs.aspx" onclick="AboutUs_Click"><span>AboutUs</span></a></li>

                 <li><a href="OurVision.aspx" onclick="Our Vision_Click"><span> OurVision</span></a></li>

               <li><a href="OurMission.aspx" onclick="OurMission.aspx_Click"><span>Our Mission</span></a></li>

                <li><a href="ContactUs.aspx" onclick="ContactUs_Click" ><span>Contact Us</span></a></li>

                  
   </ul>
   </div>
   </div>
   </div>

So, please help me, If i Mouse over on this pages, it must stay mouse over till the user goes for another page.

Thanks in Advance...................