Static Background Image?

I’d like to have a static background image for the “Dusk to Dawn” theme on my site, so that the content scrolls in front of it instead of the image repeating. I see the controls in Appearance, but they do not seem to clearly offer that option. (I’ve gotten very gunshy at just randomly trying sh*t b/c I’ve made pages or themes unmanageable by doing so.)

Thank you.

Hafizullah