这个效果怎么用css来写啊？
用 :hover a { top:0;}就可以了。
例如：
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title></title>
<link rel="stylesheet" href="style.css" />
<style type="text/css">
.time {
position: relative;
height: 400px;
width: 400px;
background: #ff6600;
overflow: hidden;
}
.time-a {
position: absolute;
top: 300px;
display: inline-block;
height: 400px;
width: 400px;
background: #000;
opacity: 0.8;
text-align: center;
}
.time:hover .time-a {
top:0;
}
</style>
</head>
<body>
<div class="content3">
<div class="time">
<a href="" class="time-a">321654987</a>
</div>
</div>
</body>
</html>