body { margin:0; padding:0; background-color: #fff; background-image:url(112.jpg); background-repeat: no-repeat; background-position: center; background-size: 80%; background-attachment: fixed;}
.dexu { display: block; position: absolute; top: 50%; left: 50%; width: 280px; height: 40px; margin: -20px 0 0 -140px;}