div居中

.bgform {    top:50%;    left:50%;    position: absolute;    /*right: 10px;*/    /*bottom: 150px;*/    background: rgba(255, 255, 255, 0.20);    border: 1px solid rgba(183, 255, 255, 0.27);    border-radius: 2px;    width: 350px;    height: 350px;    padding: 5px auto;    margin:-175px 0 0 -175px;}

来源：https://www.cnblogs.com/dog2016/p/11685463.html