Hello Noucky,
thanks for choosing Ikebana!
The live code hints that the background is not a product of the theme: the “vc” class is characteristic of the Visual Composer by WPBakery – it seems that the most likely explanation is that there’s the VC plugin installed on this website, and the grid item setting in the Visual Composer on that page generates the extra styles. Unfortunately it’s not possible to tell the exact location of the setting as I can’t see the back-end, but the place you’d have the most chances of finding it is the VC element settings (either the parent row or the element itself).
Cheers,
Andrii / Satori Studio