Hello,

The code for that html block which you pointing out in the attachment is inside the file below:

https://jmp.sh/bNuxVwe

There is no such option for “Fullscreen”. To change the width of that mega menu you have to define a custom CSS class inside the menu item and then used the below CSS code in Theme settings >> Custom CSS >> Global Custom CSS:

.controlWidth .sub-menu-dropdown{
    width: 935px !important;
}

Screenshot: https://jmp.sh/HMXyVpT

Best Regards.