1,5 years ago the VDG start with an icon theme for LibreOffice to guaranty an consistent look and feel for Plasma users. Now this new icon theme Breeze was used by default in the KDE Linux distributions and on Mac OS X.
Breeze is a monochrome icon theme and fits well into modern Desktops like Plasma and OS X but the second reason is that the Breeze icon set is a complete icon set. We can support 100 % (and I mean 100 %) of the needed LibreOffice icons. In addition Breeze supports dark colour themes AND 32 px icon size. This is unique because only the default icon set is that much feature complete.
So the breeze icons fit into modern desktop environments and are well maintained and that’s the reason Ubuntu 16.04 LTS will ship LibreOffice 5.1.1 with breeze icons for the Unity desktop.
Happy hacking the VDG,
part of the Plasma team and the KDE community