How to remove border from drop down menu

I managed to make a dropdown menu to my secondary navigation in Virtue. I also managed to change to background color, however, there is a white line around the dropdown box, and I really would like to remove it. Any one who can help?

Here is the site I am working at: https://soenderborgmusikforening.dk/

Try hover the second menu item “N?ste koncert” and you will see what I mean.

/KM