How to change colour of main menu font

Hello I'm sure it's easy for those that know how, but is there any way to change the colour of the main menu fonts. The header video i am using is very light coloured up at the top where my main menu is and it's very difficult to read the menu. Wondered if there was any additional CSS I could add to the 'additional CSS' section in the theme options. I have tried all the solutions I could find online and none seem to work. Thank you