Hi all, usually this effect appears when the stylesheet is missing or broken... However, as Anna F kindly mentioned, a missing DOCTYPE can have similar results in certain browsers (notably IE).
@izinux your server responds to the request for /wp-content/plugins/easy-fancybox/easy-fancybox.css.php (the dynamic stylesheet) with presenting the file as download instead of parsing it as a PHP file. It might be that your server configuration is thrown off course by the '.css' that is part of the file name. Are you on a shared hosting account then you might contact your provider with this issue. If you are on a (virtual) private server then you should configure the web server yourself to treat files that end with .php as PHP files even if there is '.css' in their name...
@SimonSov can you share a link?
@tglass118 looking at your site in Chrome, I see no issue. About the 'Depricated' message, you should disable the public output of errors and notices. If you cannot, you can alternatively open the file easy-fancybox.css.php (use the WordPress plugin editor) and replace the part
split( ", ", $if_none_match );
explode( ", ", $if_none_match );
(notice it is just the word 'split' that is replaced, nothing else)