Changing clicked link color, Firefox

I found a way to change the clicked link color from default to a different color. I did this because clicked links at DuckDuckGo wouldn't change color when clicked on. You have to create a folder in Owner/AppData/Roaming/Mozilla/Firefox/Profiles. You name the folder Chrome.

Then you create a ccs file in Notepad.
Change links color: Google/Firefox | Windows Secrets Lounge That explains how to do it. Here's the deal, it's every link that you click on any webpage. Annoying. I want it to work only on DuckDuckGo, not every site I visit.

Any clues what to do?

TIA