aleksandr8i,
важно ul{
position: relative;
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
ul{
position: relative;
margin:0 auto;
width:200px;
}
li{
float:left;
width:50px;
list-style:none;
}
.active{
background:#00FF00;
}
.super{
background:#FF3333;
}
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function(){
var li = $(".bg_link"), middle = $("ul").width()/2;
li.hover(function(){
var left = $(this).position().left;
$( this ).addClass(left <= middle ? "active" : "super");
},function(){
$( this ).removeClass("active super");
});
});
</script>
</head>
<body> <ul>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
<li class="bg_link">link</li>
</ul>
</body>
</html>
