Quark Default Theme Image - overview of file types?

Brand new to GRAV, familiar with PHP/CSS.

I installed GRAV plus ADMIN. The default theme is Quark, under the “Themes” left sidebar menu on the admin dashboard. Quark is shown there, with a picture as the background of the grand canyon or something.

My install has no background image. I would like to put one of my own images in there. From looking at the home page source, there’s a handful of css files there. I figured theme or spectre, so I found those files.

There’s theme.css, and theme.min.css, and spectre.css, and spectre.min.css. I’m thinking the “minified” files are just removing all the extraneous stuff that makes the regular files easy for a human to read?

Is this minified css file created from the regular file? If I edit “theme.css” will it turn into “theme.min.css”?

Or is this just now how this works at all?

Thanks for you patience as I muddle through learning GRAV!

You don’t have to mess with css.

You have to create a modular page with a “showcase” modular.