Complementary is not an icon theme, it uses Elementary OS icon theme as main theme by adding third-party application icons.
Due to Elementary OS philosophy there are not third-party icons included in it's icon theme, the aim of this project is to complement Elementary OS default icon theme following it's guidelines getting a uniform icon theme.
- Download the project from GitHub
- Copy complementary folder into ./icons folder of your home.
- run gsettings set org.gnome.desktop.interface icon-theme complementary