simple but neat

SO far it seems to work just fine. My WP-Version is 5.2.3

OTHER:
It would be cool if I could choose the z-index instead of hacking my child theme;
(my nav bar was still visible)

and it would be REALLY cool, if I could insert my own image (png, svg) into any position too! Hint Hint, lol

P.S. 3 stars because it’s simple, otherwise great little effect!