CSS: How to change colour of active navigation page menu

Question

How can i change menu background colour that is selected.

My CSS is here

 

 

.topmenu ul li a:hover,.topmenu ul li a.item_active {

background:url(images/right_798a701.png) right bottom no-repeat;

}

.topmenu ul li a:hover span,.topmenu ul li a.item_active span {

background:url(images/left_798a701.png) left bottom no-repeat;

color:#ffb3b3;

font-weight:400;

font-style:normal;

text-decoration:none;

}

 

my menu is here 

 

 

 <div class="block_10 topmenu">

<span class="preload1"></span>

         <span class="preload2"></span>

<ul id="nav">

<li><a runat="server" href="~/About" id="priv" ><span>Home</span></a></li>

<li><a runat="server" href="~/About" id="pri" ><span>Menu</span></a></li>

<li ><a href="#nogo1"><span>Promotions ▼</span></a>

<ul class="sub">

<li><a runat="server" href="~/About">Printing</a></li>

<li><a runat="server" href="~/About">Photo Framing</a></li>

<li><a runat="server" href="~/About">Retouching</a></li>

<li><a runat="server" href="~/About">Archiving</a></li>

</ul>

</li>

<li><a href="#nogo2" id="promotions" ><span >About Us ▼</span></a>

<ul class="sub">

<li><a href="#nogo19">Flash Guns</a></li>

<li><a href="#nogo20">Tripods</a></li>

<li><a href="#nogo21">Filters</a></li>

</ul>

</li>

<li><a href="#nogo22" id="services" ><span >Stores ▼</span></a>

<ul class="sub">

<li><a href="#nogo23">Printing</a></li>

<li><a href="#nogo24">Photo Framing</a></li>

<li><a href="#nogo25">Retouching</a></li>

<li><a href="#nogo26">Archiving</a></li>

</ul>

</li>

</ul>

</div>