How to disable dropdown menu of categories on ps_mainmenu

[darko2121]

I am using Prestashop 1.7.4.3 and default theme.

I want to disable dropdown menu of mainmenu. I am displaying categories on top main menu and when I hover a category, subcategories shown in a dropdown menu. I want to disable that dropdown menu.

I tried adding 

.top-menu .sub-menu{display:none !important}

in the custom.css but nothing changed.

Thanks in advance!

[PPSA]

I have also been searching everywhere for an answer for this

The same thing you have done is what I have done on 1.7.4.2 and no change even with clearing the cache.