js鼠标悬浮出现遮罩层的方法

<ul class="site-tag fl"> 
        <li><a data-title="科学" href="#"><i style="background-image: url(images/xiaozhan/main_ojls_1aa6000200891260.jpg)"> 
        </i><span class="tag-tit">科学</span> </a></li> 
        <li><a data-title="动漫" href="#"><i style="background-image: url(images/xiaozhan/main_NH8v_2e310001ebd1118e.jpg)"> 
        </i><span class="tag-tit">动漫</span> </a></li> 
        <li><a data-title="生活" href="#"><i style="background-image: url(images/xiaozhan/main_OtnR_43a60000050a118c.jpg)"> 
        </i><span class="tag-tit">生活</span> </a></li> 
        <li><a data-title="插画" href="#"><i style="background-image: url(images/xiaozhan/main_UD3z_2e510002074f118e.jpg)"> 
        </i><span class="tag-tit">插画</span> </a></li> 
        <li><a data-title="音乐" href="#"><i style="background-image: url(images/xiaozhan/main_krFk_6323000018bd125d.jpg)"> 
        </i><span class="tag-tit">音乐</span> </a></li> 
        <li><a data-title="自然" href="#"><i style="background-image: url(images/xiaozhan/main_UAbs_764f0001ff601190.jpg)"> 
        </i><span class="tag-tit">自然</span> </a></li> 
</ul>

<script type="text/javascript"> 
        $(function () { 
            //遮罩层，鼠标移动上去高度变化，变清晰 
            var $site_li = $(".site-tag li"); 
            $site_li.hover(function () { 
                var indexs = $site_li.index(this); 
                $(this).css("height", "90").find(".tag-tit").css("top", "30").css("color", "#fff"); 
                //获取当前点击li元素在全部li元素中的索引 
                //alert(indexs+1); 
                $(this).prev().css("height", "30"); 
                $(this).next().css("height", "30"); 
            }, function () { 
                $site_li.css("height", "50"); 
            }); 
        }); 
 </script>

ul li{ list-style:none;} 
.site-tag{ width:200px; overflow:hidden; z-index:5;} 
.site-tag li{ position:relative; width:200px; height:50px; margin-bottom:1px; overflow:hidden;  
transition:height 0.5s ease; -webkit-transition:height 0.5s ease;  
-moz-transition:height 0.5s ease; -o-transition:height 0.5s ease;} 
.site-tag li a { color: #666; font-size: 16px; font-weight: bold;line-height: 50px;} 
.site-tag li i{ display:block; height:90px; background-position:center center; 
opacity:0.3; filter:alpha(opacity=3);  /*设置透明度*/ 
-webkit-transition:opacity 0.5 ease;   /**/ 
-webkit-filter:grayscale(60%);         /**/ 
} 
.site-tag li:hover i { opacity:0.9; -webkit-filter:grayscale(0%); transition:opacity 0.5s ease;} 
.tag-tit{ display:block; height:100px; width:700px; color:#666; font-size:14px;}                  
.site-tag li .tag-tit{ position:absolute; top:0px; left:10px; text-shadow:1px 1px 1px rgb(0,0,0,0.1);} 
a:hover .tag-tit{ text-shadow:1px 1px 1px rgb(0,0,0,0.5);}