Description of problem:
I run LibreOffice 5 with GTK3. Some toolbars are by default at the bottom of the screen. All buttons that should present some sort of color palette always opens down, which in some (bottom placement) cases makes them invisible. 

Version-Release number of selected component (if applicable):
5.0.5-2.2. I observed this bug in all libreoffice5+gtk3 versions.

How reproducible:
Open the color palette tool like "Font Color" while the toolbar is on the bottom of the screen.

Steps to Reproduce:
1. Put the toolbar containg color palette tool on the bottom of the screen.
2. Clicke the palette.
3.

Actual results:
Color picker opens down, below the bottom edge making color choice impossible.

Expected results:
The tool should open up if there is no place below. Other tools like "shapes" works well.

Additional info: