How can I set a theme in Qt Designer?

Question

I design my user interface with Qt Designer and then load the *.ui file in Python.

For buttons I want to add Icons from the Breeze theme. In Qt Designer I can add icons via "Set icon From Theme..."

But this is loading the icon from a different theme. In my Python code I select the theme via.

QtGui.QIcon.setThemeName("breeze")

And it shows it at runtime as following:

This is what I want to see in the Qt Designer as well.

Question: How can I setup Qt Designer to use the icons from the Breeze theme?

Versions:

• Qt Creator: 3.5.1 based on Qt 5.5.1
• Ubuntu: 16.04
• PySide2: 5.12.3
• Python: 2.7.12