loading效果

css样式:

.opLayer{
    background: #000;
    opacity: 0.8;
    z-index: 1;
    width: 100%;
    height: 100%;
    position: fixed;
    text-align: center;
}

.loadingImg{
    background: url("../demo/images/loading.gif") no-repeat;
    width: 16px;
    height: 16px;
    background-size: 100% 100%;
    position: absolute;
    z-index: 2;
    top:50%;
    margin-top:-8px;
}

<div class="opLayer">
    <div class="loading"><em class="loadingImg"></em></div>
</div>

其它的效果:
http://www.cnblogs.com/lhb25/p/loading-spinners-animated-with-css3.html