Does anyone here know any CSS?

On a webpage I'm building, I have a div where I want two background images. I'm trying to make a nav bar where the color fades from white to another color then back again to match the side bars below(Which also fade).
I can do one side, but I can't do both.
This website is aimed at accessibility(Meaning easy for blind people and low vision people to navigate). I need to have the background image repeating down, so when the user changes the font to be bigger, the image still goes down.

I have thought about putting the image in the html, but it won't work out like I need it to.

I hope that wasn't too confusing. Let me know if it was.