How to remove the black border around the image field

It wasn't doing this before. It just started doing it. This is within the form.

Also, I deleted my background image, but when I reopen and publish, it's still there. I know that I saved the delete action.

I am becoming extremely frustrated with this software.

Thanks

Glenna

Thank you SO much!!!

I think my problem was in not being able to locate the CSS interface.