link underline css animation code example
Example: add expanding underline on page load css
#sec {
display: inline-block;
position: relative;
padding-bottom: 3px;
}
#sec:after {
content: '';
display: block;
margin: auto;
height: 3px;
width: 0px;
background: transparent;
transition: width .5s ease, background-color .5s ease;
}
#sec:hover:after {
width: 100%;
background: blue;
}