WM-Loose wrote: If you delete the custom.css file and the original state is still displayed, it is either due to the Joomla cache or browser cache. It is possible that the browser cache has not really been deleted. Try viewing the page with a different browser or a different device (tablet, smartphone).

CSS codes are better entered directly in the template options and not in the custom.css 

I cleared both Joomla cache and browser cache at least 100 times. Of course I tested with three browsers (Firefox, Edge, Chrome) everywhere the same result. You point out that it is better to enter CSS code directly in the template options and not in the custom.css. In fact, when I do so, it works! I will never use this custom.css file again. But the odd thing is: why on earth did the custom.css file work perfectly until Monday morning and stopped from being relevant ever since?

Anyway, thank you for the recommendation to enter CSS code to the template options. Finally this was successful and the nightmare has come to an end.

Hi.

I have a question: what is the position (folder) of your CUSTOM.CSS file?

Recently i noted that there are two position for this file: 

into MEDIA/TEMPLATES/SITE/nameofyourtemplate/CSS

and into  TEMPLATES/nameofyourtemplate/CSS

but ONLY into media folder the css file works fine...

lo, yes youre right, the custom.css should be in