ethereal,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.item{
height: 25px;
background-color: #FF0000;
}
.item.new-class{
background-color: #7B68EE;
}
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>
$(function() {
var count = 2;
//$(`.list .item:lt(${count})`).addClass('new-class');
var items = $(`.list .item`);
items
.each((i, el) => el.style.zIndex = `${(items.length - i) * 10}`)
.slice(0, count).addClass('new-class');
});
</script>
</head>
<body>
<div class="list">
<div class="item">1</div>
<div class="item">2</div>
<div class="item">3</div>
<div class="item">4</div>
<div class="item">5</div>
</div>
</body>
</html>