how to define url in background-image when image is not from public folder

- public
 - src
   - assets
      - icons
        - plus-purple.svg

This is my file structure at the moment.

I have to use 'background-image:url()' css property now.

I don’t know what the correct url link would be, if I wanna import plus-purple.svg in mycase.

My bottom line is that,
I’d like to know proper url link when I try to import image from NOT public folder! (for my background-image css property)

thank you so much!

I’M USING NEXT.JS btw!