Divi Theme header has a small grey line at the bottom that divided the main menu from the content. This “shadow” at the bottom of the header can be removed, just use the following CSS:
#main-header { box-shadow: none !important; }
If you want to remove the shadow bottom from Menu FIXED header, add this CSS code:
#main-header.et-fixed-header { box-shadow: none !important; }
CSS code for DIVI mobile header menu:
@media only screen and (max-width: 600px) {
#main-header { box-shadow: none !important; }
}