[Theme: Twenty Twelve] How to change the font color of sub-menu items

I’ve used style.css in my twenty twelve child theme to change the appearance of the navigation menu bar. The main bar now has white fonts on a green background, but the submenu items have kept their original styling (dark font on light background).

When a page is selected from one of the submenus, the text in the main menu bar turns to bold (which is good), but the text in the submenu turns white (which is wrong) and bold (which is good). So when you look at the related drop-down submenu again, it is now hard to see the word.

Is there a way in the syle.css to keep the font color of the selected submenu item black? Hope you can help.

the website: https://wijkraaddeblaak.nl/wpblaak