<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style>
.red{
background-color: #FF0000;
}
</style>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script>
$(function() {
$(".slider-one-item").slice(1,-1).addClass("red");
});
</script>
</head>
<body>
<ul>
<li class="slider-one-item">Item 1</li>
<li class="slider-one-item">Item 2</li>
<li class="slider-one-item">Item 3</li>
<li class="slider-one-item">Item 4</li>
<li class="slider-one-item">Item 5</li>
<li class="slider-one-item">Item 6</li>
</ul>
</body>
</html>