Check if its the facebook canvas

I have a website which utilizes facebook integration. You can use it independently of FB. However, it also loads in FB through the can开发者_Go百科vas page. I want to load a different CSS file if the page is being displayed on the canvas page then when it is displayed through going to it directly.

How can I check if the page loaded in the canvas page?

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Check if the fb_sig_iframe_key parameter is in the querystring. PHP would be:

if($_GET['fb_sig_iframe_key']) // Include CSS Here