If you wish to hide full_width shortcode background images on mobile devices, please use this custom CSS. Copy and paste it into the CSS field in Theme Options or if it’s specific to a single page you can add it in the code section of the containder ( </> Blue bar) .
@media only screen and ( max-width: 640px ) {
.fullwidth-box {
background-image: none !important;
}
}
And you can adjust the max-width to your desired width