Hello @Johndoan ,
I checked out the version 15.6, and the buttons are not supposed to be black, as you can see in the screenshot below.
I just checked again on android - chrome and the color is the same as above.
I suppose the color issue is related to the functionality issue, however I can’t say anything for sure.
I think you might have some content that modifies these navigation bar items, but without more info I can’t help you more. You’ll need to do some investigating yourself 
I recommend to inspect the HTML structure of that element (on firefox, right click → Q) and compare it with the one I displayed on the screenshot above. Then try to figure out where is the content that messes those buttons on your distribution, and fix it accordingly.
Have a good day,
Lucas.