Customizing .catchresponsive-nav-menu and outline

Hi Support, I'm needing some help on some custom css (preferably). This my site: http://tuanzbuild.tuanz.org.nz (still a work in progress). Where the black colour is showing in the main nav menu, I want to be able to preferably make it clear/or transparent. And make only the horizontal outlining of nav menu visiable (black). I am wanting a main nav menu like our client's old site here: http://tuanz.org.nz/ where JUST the horizontal outlining of the navigation menu is visable Could someone assist me with this please?