From The Document Foundation Wiki
From version 4.0 LibreOffice can be customized:▸ ▸ ▸ allows you to choose between Default look, Pre-installed Theme, Own Theme
For earlier versions, the visual appearance changes was limited to the buttons:
- Select the menu ▸ .
- In the left menu, select ▸ .
- In the Size and Icons Style area, select the theme and possibly change the size.
- Confirm by OK.