void parseButton_Click(object sender, EventArgs e)
{
   AylarSolutions.Highlight.Highlighter h = new AylarSolutions.Highlight.Highlighter();
   h.ConfigurationFile = Server.MapPath("CodeHighlightDefinitions.xml");
   h.OutputType = AylarSolutions.Highlight.OutputType.Html;
   string result = h.Highlight(sourceTextBox.Text, languageDropDown.SelectedValue);
   result = result.Replace("\t", "    ");
   result = result.Replace(Environment.NewLine, "<br>");
   resultLabel.Text = result;
   codeText.Text = "<p>" + result + "</p>";
}

All you have to do is replace the line:

codeText.Text = "<p>" + result + "</p>";

With this:

Now add the class into your template css and that's it!

* I'm using: