Would probably be preferable, since auto makes it behave like no z-index property has been specified (as is the case in the default Bootstrap theme used in lavender and persona) which makes the element inherit the z-index of its parent, whereas z-index: 0 forces the z-index to be, well, 0.
Hi all, today I just installed a cloud version and I can't change files myself. Faced with the same problem. I've changed the theme back to Persona and now can open no frontend nigher backend. It forwards me to the nodebb website and shows this message:
We couldn't reach the website you were looking to access. It may be offline temporarily, please try again later.