Hi Andrea.

The code that you use is the code that I wrote for a long time.

Now I have a new, simpler version. I suggest you use it instead of old code.

Here

.sppb-article-section {
    margin-left: -15px !important;
    margin-right: -15px !important;
}
@media (min-width: 576px) {
    .sppb-article-section {
        margin-left: calc(-100vw + 50%) !important;
        margin-right: calc(-100vw + 50%) !important;
    }
}
.sppb-article-section.__fluid .sppb-row-container {
    max-width: 100vw !important;
}

To get section with full width background use this class in section's CSS Class field:

sppb-article-section

To get fluid section with full width background use this classes (separated by space) in section's CSS Class field:

sppb-article-section __fluid