I can change filename's colors with that css file. (gtk.css)
But I can't set the font or bold property, it is still default font and bold.
How can I change font familiy or font weight? Thanks! - ( Eg. Image of my desktop: )
The desktop font's key location in dconf database has been changed. To change desktop font in Ubuntu 16.04 or later use this command
gsettings set org.gnome.nautilus.desktop font 'Noto Sans 11'
Here I used Noto Sans as the font and 11 as size. Use any other font and size you use. If you want to use bold variant, add bold after the font name in the command.
Same can be done using dconf-editor by navigating to the respective directories.