html,body,div,main,img,ul,ol,li,table,tr,td,header,nav,footer,aside{
    position: relative;
}
body{
    width: 100%;
    font-family: "microsoft yahei";
    color: #1a1a1a;
    margin: 0;
}

.bc{
    z-index: -1;
}
.all{
    width: 100%;
}
.left{
    float: left;
}
.right{
    float: right;
}
.clear{
    clear: both;
}