Change color of menu links

Hello everyone,

I tried to change the color of the menu links on my website. They are currently dark grey/black and I want to change them into white. I tried to change this via two ways: I changed the color to white in the design options and also in the CSS. Following class:

#core_menu_wrapper .nav > li > a {
text-transform: uppercase;
font-size:17px;
padding:20px;
color: #fff;
}

I also tried several other classes, but no result. Who can help me out?

Kind Regards,

Thomas