roundcube-easy-unsubscribe/easy_unsubscribe.css

.easy_unsubscribe_link img {
    height: 20px;
    margin-left: 10px;
    vertical-align: middle;
    opacity: 0.5;
    transition: all 0.3s ease;
    cursor: pointer;
}

.easy_unsubscribe_link:hover img {
    opacity: 1;
}