HeadlessChrome chrome = new HeadlessChrome(
    HeadlessChrome.DefaultAppPathMac
);
using (chrome) {
    chrome.Start();
    var doc = chrome.DOM.GetDocument();
    Console.WriteLine(doc);
}

HeadlessChrome chrome = new HeadlessChrome(
    HeadlessChrome.DefaultAppPathMac
);
using (chrome) {
    chrome.Start();
    var doc = chrome.DOM.GetDocument();
    var html = chrome.DOM.QuerySelector(
        doc.Root.NodeId,
        "html"
    );
    Console.WriteLine(html);
}