As for html to excel with formatting issue, you can see below code:
Response.Buffer = true;
Response.ContentEncoding = System.Text.Encoding.UTF8;
Response.ContentType = ""application/ms-excel";;
this.EnableViewState = false;
The "ContentType" property which the default set is text/HTML can help us a lot. And hypertext will be exported to client. If we change it to ms-excel, it will be exported as Excel format and your browser will remind you to download and store it. The property of "ContentType" includes image/JPEG, text/HTML, image/GIF and vnd.ms-excel/msword.