Change custom theme Background

is there is a way to change the custom themes background?
i need to put a logo at the background of the themes to be able to print with the invoices and statements …etc
can someone providing me with the code?
please help

Search the forum before posting new questions. Examples have been given in the past.

unfortunately didn’t find, would you refer that post, please

Sorry, but I am not your search engine. Try “watermark,” “background image,” and things like that.

i asked you nicely , no need to be (tough) with me. cause I thought you saw it lately, anyhow thank you

No, it was a couple years ago.