Is there any code to put in CSS in order the links to open in a new window?

Is there any code to put in CSS in order the links to open in a new window?
(similar to target _blank in a css file)

I'm guessing you meant “similar to target _blank in [an HTML] file”. No, you can't do this with CSS. You need to use either the target attribute or JavaScript.

My personal take is that you shouldn't mess with the user's preferences this regard: if the user clicks normally the content should open in the same window; if the user Shift+left-clicks, the content should open in a new window; and if the user Ctrl+left-clicks or middle-clicks, content should open in a new tab. In other words, let the user decide.

What a stupid question i was asking some months ago :D :D :D :D

I agree with Arbitrator here, let the user decide.

The user can decide anyway since at least some modern browsers allow you to configure for yourself how you want different links to work regardless of how the author coded them.