Remove the below from your aspx page as you are using master page.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<link href="CSS/Style.css" type="text/css" rel="Stylesheet" />
</head>
<body dir="rtl">
<form id="form1" runat="server">
</form>