Click the button to perform the submission operation. After the message box pops up, the style of the page changes. The solution is as follows: First, make sure that the css style is correct and that the width and height values in the page are consistent with specification 1. The pop-up box then avoids Response.Write (), as shown below

Response.Write("<script language=javascript>");
Response.Write("window.alert('");
Response.Write(" Plan to add failed! ");
Response.Write("');");
Response.Write("</script>");
 Is amended as: ClientScript.RegisterStartupScript(GetType(), "", "window.alert(' Plan to add failed! ');", true);