css样式添加遮罩

借鉴地址：“http://blog.csdn.net/sinat_31016743/article/details/53522677”

原理：利用css样式实现鼠标移入加一层遮罩的效果。将遮罩层absolute定位到要添加遮罩层的上面，鼠标移入让他显示。

代码片：
html:

<div class="ai_demo" >  
    <div class="price">  
        <div class="content">  
        <p class="price">Huskiep>  
            <p class="intro">  introduction introduction introductionp>  
        div>  
    div>  
    <div class="btn"><a href="#">like it?a><a href="#">hate it?a><a href="#">buy it!a>div>  
div> 

CSS

.ai_demo{width: 250px; height: 250px; background:url("http://www.magpet.cn/images/upload/Image/87076179_snap(25).jpg")  no-repeat scroll 0 0/100% 100% content-box content-box; background:url("http://www.magpet.cn/images/upload/Image/87076179_snap(25).jpg") 50% 50% \9;  position: relative;}  
     .ai_demo .btn{ padding: 225px 0 0 80px; text-align: right; position: relative;z-index: 999;}  
     .ai_demo .btn > a{ line-height: 22px; padding:3px 5px; margin-right: 1px; color: #fff; background: #84654e; font-size: 12px; text-decoration: none;}  
     .ai_demo div.price{ display: none;}  
     .ai_demo:hover  div.price > .content{  padding-top:70px; text-align: center;}  
     .ai_demo:hover  div.price > .content p.price,.ai_demo:hover  div.price > .content p.intro{ color: #fff; padding: 0 5%; font-size: 24px;}  
     .ai_demo:hover  div.price > .content p.intro{ font-size: 14px;}  
     .ai_demo:hover  div.price{ width: 100%; height: 250px; display: block; background: #000; opacity: .5; -moz-opacity: .5; filter:alpha(opacity=50); position: absolute; top: 0; left: 0;}