Background image withoutboxed layout is impossible

Hi,
yes, becuase of width of container.

But anytime you can add bg image using custom CSS, just use simple CSS.

For example set BG Image for that ID

#sp-main-body { }

and before you would ask me how? Read:

• https://www.w3schools.com/css/css_background_image.asp
• https://developer.mozilla.org/en-US/docs/Web/CSS/background-image

Oh.... we cannot teach CSS here for obvious reasons :/

For example

#sp-main-body { 
  background-image: url("images/background.jpg");
    background-repeat: no-repeat;  
    background-position: top; }

rename file name used in my example to current one, images/Foto-sala-per-sezione-Teatro-1.jpg

https://www.w3schools.com/css/tryit.asp?filename=trycss_background-image_position

there are tons of guides in Italian language, you can still learn new things.

OK, I will check what you did wrong.

Now is working fine, you have bg image on subpages. I guess you updated CSS.

but please improve (increase) contrast between bg color and font color, now is TOO LOW.

Think about accessibility - also older people with weak eyes. It's hard to read for them.