Darko is an icon pack. It is not a stand alone application, you need a third party launcher to apply it.
Darko: A dark set with shadow for depth. Use it with any dark wallpaper for better depth effect.
★ 2.700 + HD icons (256×256)
★ 120+ matching HD cloud wallpapers!
★ Launchers support: Action, Adw, AdwEX, Apex, Atom, Aviate, GO, Next,Nova, Smart, Solo…
★ Icon masking for un-themed icons
★ Dynamic calendar (For Nova Launcher)
★ Alternative icons to choose