The proper way to use it in a Page you will need to have the whois index.php file re-written to fit XenForo's format, and have your page call it using a phpcall back method. The input field will then be sanitized on submission. And because it is using "Post", XF's token will need to be sent with the form data.
If you do not want to do that, just add some CSS to the outputted form and make it reflect your site's theme,