... AT LINE 353 of CODEPEN LINK
.on("mousemove", function(d) {
        var html = "";

        html += "<div class="tooltip_kv">";
        html += "<span class="tooltip_key">";
        html += id_name_map[d.id];
        html += "</span>";
        html += "<span class="tooltip_value">";
        html += valueById.get(d.id);
        html += "";
        html += "</span>";
        html += "</div>";

        $("#tooltip-container").html(html);
        $(this).attr("fill-opacity", "0.8");
        $("#tooltip-container").show(); ...