Sticky Navbar with background color change and also links color

Hi There!

I am new on webflow, I can’t figure it out that how can I change the background and also the nav links colors while scrolling.

one more thing is I set the position of nav bar relative and give it z-index to auto, I did it because I want some hero Banner pic behind the nav bar as per the design requirement, but now I want nav bar sticky and when I give it to the position sticky and like z-index 999, it works but the hero banner pics which displays behind the nav bar just disappears…

So can someone help me out like what I am doing wrong?

Here is my website link (