<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title></title>
</head>
<style type="text/css">
* {
margin: 0;
padding: 0;
}
.main {
width: 1440px;
height: 4694px;
}
.sort-box {
width: 100%;
height: 90px;
background-color: aqua;
}
.3Dimg_box {
width: 1220px;
height: 500px;
background-color: #6495ED;
}
</style>
<body>
<div class="main">
<div class="sort-box">
</div>
<div class="3Dimg_box">
<a href="">这个DIV的CSS怎么没效果</a>
</div>
</div>
</body>
</html>
这个是CSS类命名问题:不能以数字开头命名CSS类

改成threeDimg_box就可以了