Text that can be copy/pasted without any formatting showing

I’ve got a section on my site where users can copy the text to be pasted (affiliate code), but I’m having trouble as it is copying all the formatting of the text as well as the text itself.

I tried preformatted, but on the theme these shows in a grey box, so when copying the text, it also shows the grey box when posting.

Is there a way I can sort this out?

Thanks.