JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/c3/0.4.10/c3.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/c3/0.4.10/c3.min.js"></script>
<div id="chart"></div>

JavaScript

var chart = c3.generate({
    data: {
        columns: [
            ['data1', 30, 200, 100, 400, 150, 250],
            ['data2', 50, 20, 10, 40, 15, 25]
        ]
    },
    tooltip: {
        contents: function (d, defaultTitleFormat, defaultValueFormat, color) {
            var sum = 0;
            d.forEach(function (e) {
                sum += e.value
            })
            defaultTitleFormat = function () {
                return sum
            };
            return c3.chart.internal.fn.getTooltipContent.apply(this, arguments);
        }
    }
});