kvizor34,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<style type="text/css">
li{
width: 100px;
height: 20px;
border: 1px dashed Gray;
padding: 5px;
}
.red{
background-color: Red;
}
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
$("ul").on("click", "li", addCls);
function addCls()
{
var el = $(this), cls = ":not(." + this.className +")";
el.nextUntil(cls).add(el.prevUntil(cls)).addClass("red")
}
})
</script>
</head>
<body>
<ul>
<li class="slonik"></li>
<li class="begemotik"></li>
<li class="begemotik"></li>
<li class="begemotik"></li>
<li class="slonik"></li>
<li class="slonik"></li>
<li class="slonik"></li>
<li class="begemotik"></li>
<li class="begemotik"></li>
</ul>
</body>
</html>