This is most likely because the css files are not writeable. Make sure you chmod the plugins/ajax-search-pro/css directory to 777.
Alternatively you can enable inline styles on the “compatibility settings” tab. It should solve the issue right away 🙂 It's available from version 2.1, which was uploaded to codecanyon 2 days ago.
Let me know how it goes!Best,
If you like my products, don't forget to rate them on codecanyon :)