Ninja Menus is a powerful Magento 2 mega menu extension that gives you the ability to create any menu quickly with zero coding. And of course, to style your menus beautifully, there is no need to add CSS. Everything will be done in a wink of an eye.
https://www.magezon.com/magento-2-mega-menu.html

To design a menu in Ninja Menus, please follow these below steps:
1. Go to the edit page of a menu (Supposed that you created a menu using Ninja Menus).
2. Open General > Styling tab where you can customize these options:
- Main Font Size / Main Font Weight: set font size and font weight of the menu of highest level.
- Main Color / Main Hover Color: color / color on hover of the text in the menu of highest level.
- Main Background Color / Main Hover Background Color: color / color on hover of the background of each item in the menu of highest level.
- Secondary Color / Secondary Hover Color: color / color on hover of the text in submenus.
- Secondary Background Color / Secondary Hover Background Color: color / color on hover of the background of each item in submenus.