How to change menus active link font color?

Hello

I'm using wordpress and I'd like to change the main menus active link font color with css, because the default setting setting isn't working.

I'm using this code:

#main-nav li a:hover {
  color: #ffffff;
}

To change the hover color, and I can't imagine the active link color would be too much different. Can someone please help me out? I'd sincerely appreciate any assistance I can get

Thannk you for your time
Peter