.links {
    position: fixed;
    top: 220px;
    right: 20px;
    z-index: 9999;
    transition: filter 0.3s ease;
}

    .links a {
        display: block;
    }

        .links a:hover {
            filter: brightness(80%);
        }

        .links a img {
            opacity: 0.7;
            box-shadow: 6px 6px 12px #555;
        }