Unable to set active status on primary links tabs

I can not figure out what I'm doing wrong here. I have messed with this for way too long already, and I just keep running in circles. I think I have it fixed, but I don't. Apparently, I just don't know what I'm doing.

What I'm trying to do is set the active primary link tab to be the same as it is with a hover. I can get the right side fine, but the left side image is eluding me. Anyone know what I need to do?

For the right, I can just do this:

#primary-links li:hover  a, #primary-links a.active {
  color: #303a49;
  background: url(images/primary-hover-r.png) right top no-repeat;
}

But that leaves the left side image the same is it is without the hover. What needs to happen for the left? I assume it needs to be here:

#primary-links li:hover {
  background: url(images/primary-hover-l.png) left top no-repeat;
}

But WHAT needs to be there?