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

SQSP has two general help articles on this:
(1) Uploading and Managing Files, and
(2) Creating a Text Link.

In each case the tactic is to upload the file, images only in method (1), capture the SQSP generated URL to the file and then use that URL in the code

<img>

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