addClass (controls) {
      const settings = Glide.settings
      const item = controls[Glide.index]

      if (!item) {
        return
      }

      item.classList.add(settings.classes.nav.active)

      siblings(item).forEach(sibling => {
        sibling.classList.remove(settings.classes.nav.active)
      })
    }
Toggles active class on items inside navigation.

@param  {HTMLElement} controls
@return {Void}