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.flex {
            /*flex 布局*/
            display: flex;
            /*实现垂直居中*/
            align-items: center;
            /*实现水平居中*/
            justify-content: center;
            text-align: justify;
            width: 100%;
            height: 100%;
            background: rgba(255,255,255,0.2);
            margin: -10px auto;
            color: #fff;
            position: fixed;
            z-index: 9999
        }

<div class="flex">
        <div>
            <img src="http://www.sucaijishi.com/uploadfile/2014/0524/20140524124241131.gif" alt="Alternate Text" />
        </div>
    </div>