Mega menu how to?

Hi,

I want to make my “Review” button on the menu to be have a bunch of categories in it. Can someone tell me how to do this with CSS?
Here is link to my site: https://www.iappadapt.com

Here is link to what I am looking for: https://www.siteiq.net/wp-content/uploads/2010/02/4.10-juniper.net-home-page1.jpg

thank you