Menu drop-down not working

Hi,

I’m working on a change to a webpage. It was originally a one-page design, but now needs to be a full webpage with a lot of subpages – so I need a menu with a drop-down submenu.
The theme I’m using is a child theme of the theme Patti that someone else made (it’s a long story…) and somehow the drop-down function isn’t working. I’ve tried various pre-made css codes that SHOULD make it work, but either the submenu doesn’t show at all at hover over or it shows but disappears as soon as I try to move my mouse to any of the submenu links. I’ve done a lot of searching and found similar issues but none of the fixes work. I suspect some other code in my theme is messing with the menu, but I can’t find it.
Long story short: I’m close to giving up and feel like I can’t see the forrest because of all the trees >.<

Below my current CSS, which doesn’t work. Like I said, I tried many, am open to try more! The webpage: https://romowind.com/test/
It’s the top menu – it’s supposed to have a dropdown for “Who we are”, “Knowledge center” etc.

#menu-top-menu-sept-2015   {

	    height: 30px; 

	    margin: 0 0 10px;
}

	#menu-top-menu-sept-2015 ul    {

	    margin: 0; padding: 0;

	}

	#menu-top-menu-sept-2015 li    {

	    display: block;

	    float: left;

	    line-height: 30px; 

	    height: 30px;

	    margin: 0; padding: 0;

	    position: relative;

	}

	#menu-top-menu-sept-2015 li a  {

	    display: block;

	    height: 30px;

	    line-height: 30px;

	    padding: 0 15px;

	}

	#menu-top-menu-sept-2015 .current-menu-item a, #menu-top-menu-sept-2015 .current_page_item a, #menu-top-menu-sept-2015 a:hover {

	    color: #000;

	    background: #ccc;

	}

	#menu-top-menu-sept-2015 ul { 

	    display: none; 

	    position: absolute;

	    top: 30px; 

	}

	#menu-top-menu-sept-2015 ul li { 

	    float: none; 

	    width: 150px; 

	}

	#menu-top-menu-sept-2015 ul li a { 

	    padding: 5px 10px;

	}
#menu-top-menu-sept-2015 ul li:hover > ul {

	    display: block; 

	}