Blueprint / .twig / .md for CSS background image

Hello
I would like to be able to select an image in the page admin, which then displays within a template div as a css background-image.

There is an incomplete solution here, which I've tried without success: /forum/archive/how-to-have-a-css-background-image-from-form-field-t8268

Can anyone please help with the correct blueprint, twig and md structure?
Many thanks
Tim

If anyone needs the answer, I finally found it here: /forum/general/css-image-loading-t118
Sorry for wasted reads and thanks to poster(s) of solution.
Tim