From The Document Foundation Wiki
- Click ▸ . This will open the Options - LibreOffice dialog window.
- Click in the list on the left hand side.
- Under Icon style the dropdown box will say which icon style was selected by default. Click this dropdown "1" (on the image) and choose one of the icon styles "2"(for example, Colibre or Breeze).
- Close the dialog by clicking the 3" button. "