strange black dropdown box

Does anyone know how to change this black box around the dropdown? It only shows up when on the photos page and then hovering over the media dropdown. Thank you for any help! 

Please post the URL for a page on your site where we can see your issue.

A link to the backend of the your site won’t work for us, i.e. a url that contains /config/.

Please set up a site-wide password, if your site is not public and you've not already done so.

Post the password here.

Adding a site-wide password does not allow anyone to alter your site. It only allows those with the password to see your site.

Please read the site-wide password and how to share a link documentation to understand how they work.

We can then take a look at your issue.

You may find How to post a forum question post useful.

Thank you Creedon for the helpful links and advice!

https://www.mickholsbeke.com/
Password: mick 

The black box, only shows up when on the photos page, and then hover over the media dropdown.
A similar form of box pops up when hovering over the media page on other pages, but it's grey.

Thank you for any help! 

You are using a dynamic header. The header menu drop downs pick up the background color of the first page section background color.

You can either mange the background colors of your first page sections or perhaps use some custom CSS.

Let us know how it goes.