How to fix the drop-down menu? (gap between menu and drop-down)

Hi everyone,

firstly, I´m a pure newbie, so please try to explain everything to me like I´m 5 years old.

So! My website is here: http://mladiinfo.cz.
I use the Swift theme and as you can notice, there is a gap between menu and the drop-down. How can i fix it?

I already went through forums discussing the same problem. The thing is, they all referred to the #access code in style.css. However, I dont see anything like that in my style.css.

Perhaps I´m missing something absolutely basic, so feel free to make idiot out of me, but I really don´t know where to look anymore.

Thanks for all the response,
TH