Sorry @Ninja but you marked "solved" the discussion "Masthead Module Background image not displayed correctly" and I couldn't reply in the right section.
The suggestions you gave me only worked for the English language, not for Italian. But shouldn't what you write in custom css have an effect on everything?
The code is:
.t4-masthead .container-fluid { padding:0px;}
Can You Check please? If You choose Lyrics/Runaway Train (For example) the mashead is in the right position only with the english language. Why?