How do I create my own tooltip for a Google chart using the tail arrow?

Question

I am trying to create a custom tooptip for a Google Cline chart using the code below:

function(files, date, serverName) {
        var htmlTooltip = '<div class ="custom-tooltip"> <label class = "tooltip-label"> Files: </label><label>' + files + '</label > <br> <label class = "tooltip-label">Date:</label><label>' + date + '</label > <br> <label class="tooltip-label" >Server:</label><label id="path">' + serverName + '</label> </div>';
        return htmlTooltip;
}

I can’t create a tooltip tail arrow with direction, since the google chart displays the tooltip arrow toward the selected point.

Please give me an idea of ​​how to implement this.