<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
.descendants *
{
display: block;
border: 2px solid lightgrey;
color: lightgrey;
padding: 5px;
margin: 15px;
}
</style>
<script src="https://apps.bdimg.com/libs/jquery/2.1.4/jquery.min.js">
</script>
<script>
$(document).ready(function(){
$("div").children("p.1").css({"color":"red","border":"2px solid red"});
});
</script>
</head>
<body>
<div class="descendants" style="width:500px;">div (当前元素)
<p class="1">p (儿子元素)
<span>span (孙子元素)</span>
</p>
<p class="2">p (儿子元素)
<span>span (孙子元素)</span>
</p>
</div>
</body>
</html>