Hello,
We would recommend using the Backend editor.
Add the next code in Theme Options > Theme custom CSS:
.site-header .widget_nav_menu .sub-menu {
top: 75%;
}then this this http://prntscr.com/1096ojb
Header builder > All department > Menu dropdown > change Dropdown content Zoom.
Delete this code – http://prntscr.com/1096qwa , go to Appearance > Menus > settings of item > set Mega menu container width, for example – https://prnt.sc/1096sh1
Regards