More subtle focus indicator

The current green 1px border for the focused item is excessively opinionated (I would say it's awful but it's a matter of opinion :) ). Then one should resort to hacks like Transparent Dolphin View in kvantummanager in order to avoid looking at a useless green rectangle all the time while using dolphin. Why not change it to a subtly (but not sooo subtly) brighter version of the theme base color?

In general the green color is beautiful, of course, it's manjaro flag color. It's just that 1px rectangle. I would change it by myself if it weren't so difficult (for me) as changing a svg file.