HtmlDocument htmlDoc = webBrowser1.Document;

  private void Form1_Load(object sender, EventArgs e)
        {
            HtmlDocument htmlDoc = webBrowser1.Document;
            HtmlElementCollection btnElement = htmlDoc.GetElementsByTagName("table");
            foreach (HtmlElement temp in btnElement)
            {
                temp.OuterHtml;
            }
        }
     //    //……

     //   private void btnHilight_Click(object sender, EventArgs e)
     //    {
     //        HTMLDocument document = (HTMLDocument)webBrowser.Document.DomDocument;
     //        IHTMLDOMNode bodyNode = (IHTMLDOMNode)webBrowser.Document.Body.DomElement;
     //       string keyword = txtKeyword.Text.Trim();
     //       if (keyword == "")
     //           return;

     //        HilightText(document, bodyNode, keyword);
     //    }

     //   private void HilightText(HTMLDocument document, IHTMLDOMNode node, string keyword)
     //    {
     //       // nodeType = 3：text节点
     //       if (node.nodeType == 3)
     //        {
     //           string nodeText = node.nodeValue.ToString();
     //           // 如果找到了关键字
     //           if (nodeText.Contains(keyword))
     //            {
     //                IHTMLDOMNode parentNode = node.parentNode;
     //               // 将关键字作为分隔符，将文本分离，并逐个添加到原text节点的父节点
     //               string[] result = nodeText.Split(new string[] { keyword }, StringSplitOptions.None);
     //               for (int i = 0; i < result.Length - 1; i++)
     //                {
     //                   if (result[i] != "")
     //                    {
     //                        IHTMLDOMNode txtNode = document.createTextNode(result[i]);
     //                        parentNode.insertBefore(txtNode, node);
     //                    }
     //                    IHTMLDOMNode orgNode = document.createTextNode(keyword);
     //                    IHTMLDOMNode hilightedNode = (IHTMLDOMNode)document.createElement("SPAN");
     //                    IHTMLStyle style = ((IHTMLElement)hilightedNode).style;
     //                    style.color = "black";
     //                    style.backgroundColor = "yellow";
     //                    hilightedNode.appendChild(orgNode);

     //                    parentNode.insertBefore(hilightedNode, node);
     //                }
     //               if (result[result.Length - 1] != "")
     //                {
     //                        IHTMLDOMNode postNode = document.createTextNode(result[result.Length - 1]);
     //                        parentNode.insertBefore(postNode, node);
     //                }
     //                parentNode.removeChild(node);
     //            } // End of nodeText.Contains(keyword)
     //        }
     //       else
     //        {
     //           // 如果不是text节点，则递归搜索其子节点
     //            IHTMLDOMChildrenCollection childNodes = node.childNodes as IHTMLDOMChildrenCollection;
     //           foreach (IHTMLDOMNode n in childNodes)
     //            {
     //                HilightText(document, n, keyword);
     //            }
     //        }
     //    }
     //}