Hey guys,
thanks a lot for your answers. Unfortunatelly I am unable to find Appearanace – Customize – Additional CSS probably because I am using a Block-styled Theme which does not have this option. I can only see Editor where I could not find where to put the custom CSS code.
Also I am a bit curious how it happend in the first place because I remember it was working OK up until some point.
Thanks in advance for your feedback!
Pavel