演示：
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>Document</title>
<style>
*{
margin: 0;
padding: 0;
}
a{
display: block;
color: #090;
80px;
height: 32px;
border:1px solid #090;
text-align: center;
text-decoration: none;
line-height: 32px;
margin: 50px auto;
}
a:hover{
background:#090;
color: #fff;
}
#modal-overlay{
visibility: hidden;
position: fixed;
left: 0;
top: 0;
100%;
height: 100%;
background:rgba(0,0,0,.5);
z-index: 999;
text-align: center;
}
.modal-data{
300px;
margin: 100px auto;
background:#fff;
border:1px solid #090;
text-align: center;
}
p{
80px;
height: 32px;
line-height: 32px;
text-align: center;
margin: 20px auto;
}
</style>
</head>
<body>
<a href="javascript:;" onclick='overlay()'>模态框</a>
<div id="modal-overlay">
<div class="modal-data">
<p>模态框</p>
<a href="javascript:;" onclick='overlay()'>关闭</a>
</div>
</div>
<script>
function overlay(){
var el = document.getElementById("modal-overlay");
el.style.visibility = (el.style.visibility == "visible")?"hidden":"visible";
}
</script>
</body>
</html>