//实现局部遮罩
#box{
width:400px;
height:300px;
position:relative;
margin:0px auto;
border:1px solid #000;
}
#shade{
width:400px;
height:300px;
background-color:gray;
position:absolute;
z-index:999;
left:0px;
top:0px;
-moz-opacity:0.5;
opacity:0.5;
filter:alpha(opacity=50);
}
局部遮罩
遮罩消失
