Hello,
Add the below code to Theme Options > Custom CSS
@media only screen and (min-width: 992px) {
.header-main-menu .item-design-mega-menu .nav-sublist-dropdown {
left: 300px !important;
margin: 0 !important;
right: 0px !important;
width: 75% !important;
max-width: 75% !important;
transform: none !important;
}
.header-main-menu .item-design-mega-menu, .header-top, .header-main, .header-bottom, .header-wrapper .et_column.pos-static ~ .et_column:last-child {
position: static;
}
}
Check the menu after that. Does it suit your needs?
Regards