visjs TimeLine chart tooltip

I have a vis.js timeline chart with tooltip that shows some infos. My problem is: the tooltip is large and cannot show all the information because the bottom of the tooltip is hidden after the border of the chart box.

This is the css code:

div.vis-tooltip {
    position: ABSOLUTE;
    visibility: hidden;
    padding: 5px;
    white-space: nowrap;
    font-family: verdana;
    font-size: 14px;
    color: #000;
    background-color: #f5f4ed;
    -moz-border-radius: 3px;
    -webkit-border-radius: 3px;
    border-radius: 3px;
    border: 1px solid #808074;
    box-shadow: 3px 3px 10px rgba(0,0,0,.2);
    pointer-events: none;
    z-index: 5;
}

Try to change the css of the class "vis-timeline" :

.vis-timeline {
    position: relative;
    border: 1px solid #bfbfbf;
    overflow: hidden;  /* remove this line or add "overflow: unset !important;" */
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

Because of the overflow hidden, the full content inside the chart does not show even if you change the z-index.