GTK

Themes

Install a theme.

pacman -S arc-icon-theme arc-solid-gtk-theme

List installed GTK themes.

find $(find ~/.themes /usr/share/themes/ -wholename "*/gtk-3.0" | sed -e "s/^\(.*\)\/gtk-3.0$/\1/") -wholename "*/gtk-2.0" | sed -e "s/.*\/\(.*\)\/gtk-2.0/\1"/

Set a theme. Name of GTK theme is the folder name under /usr/share/themes/ and for the icon theme under /usr/share/icons/.

gsettings set org.gnome.desktop.interface icon-theme Arc
gsettings set org.gnome.desktop.interface gtk-theme Arc-Dark-solid