<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<style>
* {
margin: 0;
padding: 0
}
img {
vertical-align: top;
}
.main {
margin: 10px auto 0;
width: 1000px;
}
.fixed {
position: fixed;
top: 0;
left: 0;
}
</style>
<script src="../jquery-1.12.4.js"></script>
<script>
$(function () {
$(window).scroll(function () {
//判断卷去的高度超过topPart的高度
//1. 让navBar有固定定位
//2. 让mainPart有一个marginTop
if($(window).scrollTop() >= $(".top").height() ){
$(".nav").addClass("fixed");
$(".main").css("marginTop",$(".nav").height()+10);
}else {
$(".nav").removeClass("fixed");
$(".main").css("marginTop", 10);
}
});
});
</script>
</head>
<body>
<div class="top" id="topPart">
<img src="images/top.png" />
</div>
<div class="nav" id="navBar">
<img src="images/nav.png" />
</div>
<div class="main" id="mainPart">
<img src="images/main.png" />
</div>
</body>
</html>
原文：https://www.cnblogs.com/tutu3518/p/10950776.html