<a href="##">菜单</a>
//兼容IE9以上
a{
display: inline-block;
padding: 3px 12px;
text-decoration: none;
position: relative;
}
a:before{
content: "";
position: absolute;
transition: all .2s ease-in-out;
left: 50%;
right: 50%;
bottom: 0;
border-bottom: 5px solid red;
}
a:hover::before{
left: 0;
right: 0;
border-bottom-color: #009a61;
}
