<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

<title>无标题文档</title>

<style type="text/css">

div{

    width:50px;

    height:20px;

    line-height:20px;

    overflow:hidden;

    border:1px solid red;

    text-align:center;

    }

    a{

        wdith:50px;

        float:left;

        overflow:hidden;

        text-decoration:none;

        }

        span{

            margin-top:-20px;

            display:block;

            }

            a:hover{

                padding-top:20px;

                }

</style>

</head>

<body>

<div>

    <a href="#">

   <span> hover</span>

     默认

    </a>

</div>

</body>

</html>