Thanks again for the reply!
I think I managed to create the child successfully. Thanks for the links and help @wpyogi. it really helped!
As for the issue of removing the shadow/or even the complete box on the header, is there a way to do that? By the way, I just want to remove the shadow and/or the complete header oval box, but not the content (social icons and menu/pages displayed inside). Any ideas on that anyone?