Mantra Theme

Mantra Theme – can anyone tell me how to change the Home page menu tab colour and other Menu font colours. I have changed the background from white to black and now need to change the menu font colour to white.
I have tried putting in custom Css
#access ul li a { color: #aabbcc; font-family: Helvetica }
But it doesn’t change it. I have also tried this by changing menu background colour and it doesn’t work either.