Safari search results | How to improve visibility of currently selected site?

I use the keyboard up/down arrows to select web-site hits in Safari's search result list. When I get the one I want I can tap Return to open. The problem that I have is that it's difficult to see which of the sites I'm currently focussing on. There's a very faint, grey border around it. Can this be made thicker, darker, or a more distinct colour to improve visibility? The screenshot show an extreme version of what this might look like.

I don't see anything to do this in Safari Preferences/General or System Preferences/Accessibility.