Highlight words in webbrowser control

In windows forms the WebBrowser control permits to include a fully funcional browser into your application. The interesting things is that you can interact with the html of the site with no problem. As an example you can load a page and highlight some words into the text, here is the result of loading www.nablasoft.com and I want to highlight "laureati" and "passione".

As you can see I’ve highlighted the two words, the code is really simple.

private void button1_Click(object sender, EventArgs e){   webBrowser1.Navigate("http://www.nablasoft.com/");   webBrowser1.DocumentCompleted += webBrowser1_DocumentCompleted;   }void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e){   IHTMLDocument2 doc2 = webBrowser1.Document.DomDocument as IHTMLDocument2;   StringBuilder html = new StringBuilder(doc2.body.outerHTML);   var words = new[] { "laureati", "passione" };   foreach (String key in words)   {      String substitution = "<span style='background-color: rgb(255, 255, 0);'>" + key + "</span>";      html.Replace(key, substitution);   }   doc2.body.innerHTML = html.ToString();}