After upgrading from 16.04 to 18.04 (keeping my home folder) Thunar looks like this in an i3 session:
Apparently some icons are missing, but what do I have to install?
Note that the accepted answer of this older question is obsolete since package gnome-icon-theme-full
does not exist anymore. xfce4-settings-helper
doesn't seem to exist anymore, either.
Best Answer
The approach from hrzhu's answer still works:
lxappearance
.Note how the default, Adwaita, seems to be broken.