I've had a hard time finding the CSS to modify the menu

I've had a hard time finding the CSS to modify the menu from having the "/" between each page name. Also below the header and above the slider there is that black line. Where do I modify that color? Right now I have a black line but I'd like to replace it with an image but when I use CSS to put an image there the default orange line is over it.. Any help is welcome!

Tried to search for data on these issues had no luck. Thanks in advance!