To install this set, all you have to do is go to Shiira’s icon preferences, choose ‘load icons’, and navigate to the ‘ShiiraIcons.plist’ inside the Hickstheme folder. This will load the main toolbar icons. If you want to use plain folder icons to clean up the interface (along with some other improvements), these have to copied manually into > Shiira (ctrl-click to choose ‘show package contents’)> contents> resources>. Just a replacement icon for icon preferences is yet to be done.
Read: 'Shiira theme'