.anniversary-tooltip {
    position: relative;
    cursor: pointer;
}

.anniversary-tooltip:hover::after {
    content: attr(data-title);
    position: absolute;
    background-color: #333;
    color: #fff;
    padding: 5px 10px;
    border-radius: 5px;
    top: 100%;
    left: 0;
    white-space: nowrap;
    z-index: 1000;
}
ul {
   list-style: none;
   margin-left: 0;
   padding-left: 1em;
}