css loading

<style type="text/css">
.test {
position: relative;
width: 200px;
height: 200px;
margin: 100px;
border: 10px solid #f00;
}
.test-loading-img {
background: url(Css/Themes/Default/Images/ajax-loader.gif) no-repeat;
top: 0px;
left: 0px;
right: 0px;
bottom: 0px;
margin: 0px;
width: inherit;
height: inherit;
position: absolute;
background-position-x: 50%;
background-position-y: 50%;
background-color: #000;
opacity: 0.6;
}
</style>
<div id="dd" class="test">
<div>数据内容省略</div>
<div class="test-loading-img"></div>
</div>