Custom CSS for Menu Navigation

Hello,

I've added drop down menu items to the standard menu which comes with the theme Fixer. And I've noticed a black solid line appear underneath the top level items which have drop down items, I firstly wanted to get rid of this and hours of trial and error It's still not disappeared. I have pin pointed the CSS class to be something along the lines of: li.menu-item-has-children

I have edited this but somehow the CSS just keeps on getting overridden somewhere along the chain of command. As you can see from the screenshot it's the 'Services' menu item which is problem.