How can I add a background image to a code block?

Site URL: https://chihuahua-clarinet-zdjc.squarespace.com/config/

I want to add a textured background image to a code block that displays text on my home page.  How can I add the image to my website so that the url attribute in my background-image tag knows where to find it? 

Thanks, Derrick! This worked just fine, and now I know how to manage files in the future.