常见css块

清除浮动

.clearfix{
    *zoom:1;
}
.clearfix:after{
    content:"";
    display:block;
    clear: both;

    height: 0;
    visibility: hidden;
}

父元素高度已知，垂直居中

.v-center{
    position: relative;
    top:50%;
    transform: translateY(-50%);
}

父元素宽度已知，水平居中

.h-center{
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
}