Menu disappearing behind content

Hi,

The drop down menu on our site is disappearing behind the content. The menu item with the drop down list is Treatments, and there are 13 sub-items. When you view the menu, it appears behind the map on https://gmtdemo.co.uk/beauty/contact-us/, behind the accordion on https://gmtdemo.co.uk/beauty/treatments/ and mixed with the text on https://gmtdemo.co.uk/beauty/about-the-beauty-rooms/

I tried adjusting the Z-index of the navigation, but this didn’t work. Could you please advise?

.main-navigation ul ul{
position: absolute;
top: 100%;
left: 0;
width: 200px;
background: #fff;
text-align: left;
display: none;
z-index: 9999;
}

Many thanks.

The page I need help with: [log in to see the link]