Menu a:active not working?

#mainmenu-nav {
	list-style: none;
	list-style-type: none;
	width:153px;
	margin:-5px 0 7px 3px;
	padding:0;
	font-size:12px;
}
.li-nav a {
	padding: 2px 1px;
	width: 151px;
	display: block;
	text-indent:2px;
	text-decoration: none;
	margin:0;
	color:#646464;
}
.li-nav a:hover { background-color:#000; color:#fff; text-decoration:none; }
.ul-nav, .li-nav { display: block; list-style: none; }
.ul-nav { width: 153px;	padding:0; }
.li-nav {float: left; margin:0; }
 
.li-nav .ul-nav  {
	display: none;
	position: absolute;
	background-color:#c6c6c6;
	margin-left: 136px;
	margin-top: -19px;
	border-left: 1px solid #000;
	border-right: 1px solid #000;
	border-bottom: 1px solid #000;
	border-top: 4px solid #000;
	z-index: 99;
}

<ul id="mainmenu-nav" style="overflow:hidden;">
<li class="li-nav"><a href="index.php">{LANG_HOME}</a></li>
<!-- BEGIN: a -->
<!-- BEGIN: ul_start -->
<ul class="ul-nav">
<!-- END: ul_start -->
<!-- BEGIN: li_start -->
<li class="li-nav">
<!-- END: li_start -->
<a href="index.php?_a=viewCat&amp;catId={DATA.cat_id}">{DATA.cat_name}</a>
<!-- BEGIN: li_end -->
</li>
<!-- END: li_end -->
<!-- BEGIN: ul_end -->
</ul>
</li>
<!-- END: ul_end -->
<!-- END: a -->
<!-- BEGIN: gift_certificates -->
<li class="li-nav"> <a href="index.php?_a=giftCert">{LANG_GIFT_CERTS}</a></li>
<!-- END: gift_certificates -->
<!-- BEGIN: sale -->
<li class="li-nav"> <a href="index.php?_a=viewCat&amp;catId=saleItems">{LANG_SALE_ITEMS}</a></li>
<!-- END: sale -->
</ul>