一 .鼠标移入下划线向两边展开
鼠标移入下划线展开#underline{
width: 200px;
height: 50px;
background: #ddd;
margin: 20px;
position: relative;
}
#underline:after{
content: "";
width: 0;
height: 5px;
background: blue;
position: absolute;
top: 100%;
left: 50%;
transition: all .8s;
}
#underline:hover:after{
left: 0%;
width: 100%;
}
二.鼠标移入下划线由左向右展开
鼠标移入下划线展开#underline{
/* width: 200px; */
height: 50px;
background: #ddd;
margin: 20px;
position: relative;
}
#underline:after{
content: "";
width: 0;
height: 5px;
background: blue;
position: absolute;
top: 100%;
left: 0%;
transition: all .8s;
}
#underline:hover:after{
left: 0%;
width: 100%;
}
原文：https://www.cnblogs.com/hudunyu/p/12889073.html