Hi Thomas, I tried that site but can’t find any close button. In any case, you would need to resort to custom CSS to replace the FancyBox close button.
This custom CSS can be added to the theme customizer CSS field or it can be added by a plugin. This may be pure CSS or CSS with a replacement background image.
As it stands, we have a little test plugin available that is meant to be integrated into a future version of Easy FancyBox Pro. The test plugin simply replaces the default button and arrow icons with a more modern (flat) style. In this case, white on green but you could replace the images with your own…
Let me know if you would like to receive the icons plugin to play around with it 🙂