Detecting if site is inside iframe - loading custom CSS
You could...


munge the window.location object to add the additional param, but that will force the page to reload. From there you can access the param in Drupal and write server-side code to do a drupal_add_css().
Use jQuery (which comes with Drupal) to add the CSS directly.
Use jQuery to add a link to the remote stylesheet.


Example of the third method:

if (top !== self) {
  var cssURL = 'http://example.com/my/stylesheet.css';
  $('head').append('&lt;link rel="stylesheet" href="' + cssURL + '"/&gt;');
}


I would think that as long as you can predict the stylesheet name, the last option is going to be the most elegant.

Note that you would want to add the JavaScript to the document with drupal_add_js() in Drupal.