NewsShowPro GK5 - changing css does not show any effect

I am using NSP GK5 with the Quickstart of Shop&Buy template.

Changing parameters in the administrator of the module work. I am using the module mode "centered title overlay".
But I would like to change color, textsize, alignment of the Text which lays over the image. So I tried to change the parameters in STYLE.CSS of ...modules/mod_news_pro_gk5/portal_modes/centered_title_overlay .

I guess this is the correct file when using "module mode centered title overlay" to change. BUT all the changes did not show any effect on the website. Not even deleting the whole file. (if I delete controller.php - this shows an effect. so I think I am in the correct folder.)

http://www.pfaffstaller.com/2014/

thank you

First of all - making changes to core css files is a bad idea if You will ever want to do upgrade of template.
Use override.css instead and enable it in template settings.
When there will be any declarations in override.css and they will not work, please write back.