Градиент подчеркивает онлайн урок.




a {
position: relative;
padding-bottom: 2px;
text-decoration: none;
}

a:hover::after {
content: "";
position: absolute;
bottom: 2px;
left: 0;
height: 1px;
width: 100%;
background: #444;
background: linear-gradient(left, transparent 0%,#444 50%,transparent 100%);
}