First item of navigation tree is always highlighted

By default the first navigation item is highlighted in the navigation tree. When I click the second or third item in the navigation tree, the third item is highlighted, but also the first item. I have to click somewhere random on the page for the first item to be not highlighted. I don't want the first item to be highlighted when I click on the third item.   I also inspected the page. The third item receives the 'active' class when I click it, but to my surprise the first item does not have this class. This makes me very curious how the first item can be highlighted, when it does not even have the 'active' class. Does somebody know how to solve this?
1 answers

Apparently the first item of the navigation tree always had the :focus state by default. I changed the :focus in the css file so it does not look like it's highligted. This solved the issue.