<!DOCTYPEhtml>
<html>
<head>
<metacharset=”UTF-8″>
<title>鼠标移入下划线展开</title>
<styletype=”text/css”>
#underline{
width:200px;
height:50px;
background:#ddd;
margin:20px;
position:relative;
}
#underline:after{
content:””;
width:0;
height:5px;
background:blue;
position:absolute;
top:100%;
left:50%;
transition:all.8s;
}
#underline:hover:after{
left:0%;
width:100%;
}
</style>
</head>
<body>
<divid=”underline”></div>
</body>
</html>
