<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
<style>
ul>li {
background-color: #999;
margin: 20px;
}
ul>li.active{
background-color: greenyellow;
}
</style>
<script src="https://cdn.bootcss.com/jquery/3.3.1/jquery.min.js"></script>
</head>
<body>
<ul id="demo">
<li>1</li>
<li>2</li>
<li>3</li>
<li>4</li>
</ul>
</body>
<script>
$(function(){
$('#demo>li').on('click',function(){
$(this).addClass('active');
$(this).siblings().removeClass('active');
})
})
</script>
</html>
