css垂直水平居中

    .wrapper {
        position: relative;
        width: 500px;
        height: 500px;
        background-color: #ddd;
    }
    .content{
        background-color:#6699FF;
        width:200px;
        height:200px;
        position: absolute;
        /*position:absolute;*/
        left:50%;
        top:50%;
        margin-top: -100px;
        margin-left: -100px;
    }


<div class="wrapper">
    <div class="content"></div>
</div>