How do I reference an image in my theme in css?

Themes
1

So I added some icons, and would like to use them with my css classes.
But, am stuck on how to reference them in my css.

Suppose I put my icons in assets/icons/close.svg.
In my css, what’s the url?
background-image: url(<what goes here?>)

2

I assume that your css file is in /assets/css/style.css. Then you need to write background-image: url('../icons/close.svg'). Where is your css file anyway?