<a href="#" class="cp_link">リンクテキスト-link text-</a>
.cp_link {
padding: 0.1em 0.3em 0em 0.3em;
background-image: linear-gradient(rgba(0,0,0,0) 50%, rgba(33,150,244,1) 50%);
background-position: 0 0;
background-size: auto 200%;
transition: .3s;
color: #2196f4;
}
.cp_link:hover {
background-position: 0 100%;
color: #fff;
}