<a href="#" class="cp_link">リンクテキスト-link text-</a>
.cp_link {
position: relative;
padding: 0.1em 0.3em;
display: inline-block;
transition: .3s;
color: #FFA000;
}
.cp_link::after {
position: absolute;
bottom: 0;
left: 50%;
content: '';
width: 0;
height: 1px;
background-color: #FFA000;
transition: .3s;
transform: translateX(-50%);
}
.cp_link:hover::after {
width: 100%;
}