Installation Steps:

1. Open Terminal using Spotlight search by pressing  <command+space>.
   Type terminal and hit  Enter key.
2. Now, run
   ruby -e “$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)” < /dev/null 2> /dev/null
3. Install adwaita-icon-theme using brew
   brew install adwaita-icon-theme

adwaita-icon-theme is ready to use now!