Problem with submenus

Good morning and happy Christmas from Greece.
I'm using maximenu ck for a website i'm working on but i have a slight problem with the sub menus.
Please have a look at the following photos.
The first one shows the menus created by menu manager. However when i hover mouse over menu A i can't see sub menu B as you can clearly see on the second picture.

Any ideas?

Hi
thanks, happy christmas too
please give me your url to see the issue
are you sure that these items are published and accessible on all pages for all people ?
Ced

Hi Ced,
thanks for your immediate answer.
Everything is published as it should be and accessible for all.
Have a look at the page klimeco.gr/index.php

ok, do you have used the "nativejoomla" layout in the advanced options ? you must use the default layout if you want to have a dropdown menu

That's the problem... if i select "nativejoomla" i can't see a flyout menu with the links "eco", "mark 3", "mark 3 selective" etc as shown in the first photo.
However if i select "default" in the advanced options i can see my menus but the outcome is messed up..

edit:
it seems i'm on the right track. I selected the "blank" menu theme on styles options but now my dropdown menu is partially transparent. Can you help me with that?

ok,
then try to add something like this in your css: