A CSS query.

I am using a modified theme and I need a little help with CSS.

On the top navigation, when I move my mouse over the nav it changes colour which is nice, but what I want it to do is the active page to stay highlighted.

The theme developer gave me this, but I don’t know what to do with it.

ul#menu li.current_page_item { }

Here is the rest of the CSS for the menu. it's the blue colour #0099cc from hover I wish to show in the nav for the active page. I pasted that in, but wasn't enough.

#menu-wrap {
	position:absolute;
	height:30px;
	right:0;
	margin-top:-20px;
	margin-bottom:-20px;
	display:inline;
	top:50%;
	bottom:50%;
	clear:both;
	z-index:1;
}
ul#menu {
	position:relative;
	margin-left:10px;
}
ul#menu li {
	position: relative;
	display: inline;
	float: left;
	margin-left:10px;
}
ul#menu li.current_page_item a { color: #fff; }
ul#menu li a {
	display:block;
	height: 100%;
	padding:0 10px;
	text-align: left;
	line-height: 40px;
	font-size:12px;
	color:#fff;
	font-weight:normal;
	text-transform:uppercase;
	text-decoration: none;
	background: transparent url(styles/default/opacity50.png) left top repeat scroll;
}
* html ul#menu li a { display: inline-block; }
ul#menu li a:hover {
	color: #fff;
	background:#0099cc;
}
ul#menu ul {
	visibility:hidden;
	position:absolute;
	left:0;
	top:40px;
	z-index:1;
	padding-top:5px;
	width: 160px;
}
ul#menu li li {
	display:block;
	width: 100%;
	margin:0;
	cursor:pointer;
	background: transparent url(styles/default/opacity70.png) left top repeat scroll;
	border-bottom:1px solid #111;
}
ul#menu li li a {
	height:auto;
	color:#ccc;
	line-height:30px;
	font-weight:normal;
	background:none;
	text-transform:none;
	font-size:12px;
	margin:0;
}
ul#menu li li a:hover {
	color: #0099cc;
	background:#000;
}

ul#menu ul ul {
	position:absolute;
	left:100%;
	top:-1px;
	padding:0;
	width: 100%;
	visibility:hidden;
	z-index:2;
	border:1px solid #111;
}