Color of visited links difficult to see

On this web site, I am using a Corpo child theme with only 15 to 20 lines adapated compared to original Corpo.

My problem is that, in the navigation menu on top of the page, a visited link gets a color which makes the link almost become invisible.

Unfortunately, I am not very familiar with CSS. Even if i tried to use Firebug to “decode” the CSS mistery, I did not manage to find out what to change in style.css to get a color for visited links which can better be seen.

Any help is kindly appreciated. Thanks lot!