css links suspended animation

Why 80% of the code can not do farming architect? >>>  

style

Code

.site-top ul li a:after {
    content: "";
    display: block;
    position: absolute;
    bottom: -16px;
    height: 6px;
    background-color: #FE9600;
    width: 100%;
    max-width: 0;
    transition: max-width .25s ease-in-out;
}

 

Reproduced in: https: //my.oschina.net/lemos/blog/3057157