Fancy Drop Down Menu

I have this rough draft of a dropdown i been trying to make. As you can see theres a number of columns. I try to keep the top divs of the column of a ratio of 10/6 And whatever the height is of that box, i want the dropdown element's max height to be that. Yet for some reason im having the hardest time getting this all together. I got something that almost worked except its waaay to buggy to use, and it uses js scripts which i would rather avoid for something as simple as this. I assume i can make it the same as any other nav drop down but idk how to work with the heights, due to the aspect-ratio i cant use percents for both width and height it seems. Also, any tips on how i should lay this html out? I think i got it, but might be messy. For now im thinking of putting each column in its own div and those in a container div(outer most box in image) and using a flex layout on that. Other than that the dropdown divs are a mystery to me xD