CSS常用选择器记录-:nth-of-type(n)

.step_icon3 li.item{
    width: 30%;
    height: 40px;
    text-align: center;
    padding-top: 10px -5px 0px;
}
.step_icon3 li.item:nth-of-type(1){
    background:url(../img/find_pw_on_1.png)  no-repeat center right;
    background-size: 27px auto;
}

.step_icon3 li.item:nth-of-type(2){
    background:url(../img/find_pw_off_2.png)  no-repeat center center;
    background-size: 27px auto;
}
.step_icon3 li.item:nth-of-type(3){
    background:url(../img/icon_s3.png)  no-repeat center left;
    background-size: 27px auto;
}