蒙版：就是在图片上添加一个图层，用于美化页面，增加页面的可读性
<!DOCTYPE html>
<html>
<head lang="en">
<meta charset="UTF-8">
<title></title>
<style>
div{
width: 300px;
height: 300px;
overflow: hidden;
position: relative;
margin: auto;
}
div p{
display: block;
width: 300px;
height:100px;
background: rgba(0,0,0,.4);
bottom: 20px;
left: 0;
position: absolute; }
div p:hover{
bottom: -30px;
color: black;
} </style>
</head>
<body>
<div>
<img src="图片路径" alt="#"/>
<p>蒙版</p>
</div>
</body>
</html>
