@media print styling

Which layout do you use? Double sidebar with one sidebar on each side?

Try something like:

.col-3cm .main-inner { padding-left: 0; padding-right: 0; }

does not work
I use two sidebars on the left
with your css, layout is completely broken

I mean on the right, the sidebars are on the right sorry

What happens if you do:

.col-3cl .main-inner { background: none; padding-right: 0; }

it works on the basic page template with two sidebars on the right but if I try to print a single post page, it leaves half of the printed page empty, it does not expand to the right as on the basic template

Try applying it for all layouts:

.main-inner { background: none!important; padding: 0!important; }

this works, thank you