Hey Lawrence,
Thanks for writing in! Unfortunately, you cannot change any of the CSS for the content within an <iframe> from your site unless you have control of the <iframe> content yourself. For example, your domain is http://www.myinsuranceplanner.co.uk/ and if you are iframing in content from http://google.com/, you will not be able to control any of the content from http://google.com/ because CSS does not work cross-domain in this way. This is not a matter of how the theme operates, instead it is a matter of the HTML/CSS spec set forth by the W3C.
Thanks!