Created this css thanks to this forum. There is just a dot icon to show open folders. I have been using it for half a year and really like it. Maybe there are some ideas or ways to improve it.
There are a lot of commented css blocks because it used to be a rainbow like file explorer 
and these css can still be used to tweak the appearance. The idea was that collapsed folders had no colors or icons. But each level of an open folder had it’s own color. Until an update broke it. 
file-manager-3.03.css (3.8 KB)