get defaultContent() {}

grid.customDrawHeader.addEventListener(function (sender, args)
{
    var div = document.createElement("div");
    div.style.backgroundColor = "darkcyan";
    div.style.color = "#fff";
    div.style.textAlign = "center";
    div.style.fontSize = "larger";
    div.style.padding = "10px 5px";
    div.style.borderRadius = "5px";

    if (args.column === 4 || args.column === 5)
    {
        var button = document.createElement("button");
        button.innerHTML = "Σ";
        button.style.float = "left";
        button.addEventListener("click", (e) => { e.stopPropagation(); showSum(args.column) });
        div.appendChild(button);
    }

    div.appendChild(args.defaultContent);
    args.content = div;
});