.tooltip-overlay {
    position: relative; 
    display: inline-block;
}

.tooltip-overlay .popup {
    position: absolute;
    bottom: 100%;
    min-width: 30px;
    padding: 5px;
    margin: 0;
    font-size: 13px;
    opacity: 0;
    transition: opacity 500ms 1s;
}

.tooltip-overlay .popup.visible {
    opacity: 1;
    transition: opacity 500ms;
}