标题文字下加横线 使用:after属性

nytitle{ font-size: 30px;
color: #004a84;
font-weight: bold;
line-height: 38px;
position: relative;
padding-bottom: 10px;
display: block;
margin-bottom: 10px;}

.nytitle:after {
position: absolute;
content: '';
height: 3px;
margin: 0 auto;
width: 50px;
background: #004a84;
-o-transition: .5s;
-ms-transition: .5s;
-moz-transition: .5s;
-webkit-transition: .5s;
transition: .5s;
bottom: 0px;
}

.nytitle:hover:after {width: 80%;background: orange;}