1、实现原理：利用JS给body换背景图片，核心语句：
document.body.style.backgroundImage = "url(路径)";2、整体代码：
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<style>
*{margin:0;padding:0}
body {
background: url(images/1.jpg) top center;
}
.box {
height: 150px;
background: rgba(255,255,255,.3);
text-align: center;
padding-top:50px;
}
.box img {
cursor: pointer;
}
</style>
<script>
window.onload = function(){
var pic1 = document.getElementById("pic1");
var pic2 = document.getElementById("pic2");
var pic3 = document.getElementById("pic3");
pic1.onclick = function(){
document.body.style.backgroundImage = "url(images/1.jpg)";
}
pic2.onclick = function(){
document.body.style.backgroundImage = "url(images/2.jpg)";
}
pic3.onclick = function(){
document.body.style.backgroundImage = "url(images/3.jpg)";
}
}
</script>
</head>
<body>
<div class="box">
<img src="images/1.jpg" alt="" width="150" id="pic1"/>
<img src="images/2.jpg" alt="" width="150" id="pic2"/>
<img src="images/3.jpg" alt="" width="150" id="pic3"/>
</div>
</body>
</html>