I saw a quite unpleasant problem with formal white and I wonder where am I supposed to look for the solution.
It is a couple of years I usually have Setting > Site Administration > Appearance > Themes > Theme settings > Theme designer mode = ON is spite of defaults.
I usually use formal_white as working theme and all is fine with it. Yesterday, for some not relevan reasons, I switched "Theme designer mode" to off.
Attached are two screen shot of my local Moodle home page with "Theme designer mode" ON and OFF.
Where, this strange issue in the category background image, may come from?
Any help is appreciated.
Thanks in advance