Run the UI files through `gtk-builder-tool simplify --3to4` to update the layout properties.
The remaining difference here is GtkArrow, which is deprecated and has not been updated to the latest CSS rendering standards.
The reftest broke when font size lead to labels > 16px.
This test is a bit brittle because it doesn't properly rely on CSS properties but needs to use widget style properties to turn of extra sizing from widgets. It might break in the future when porting widgets to draw properly.
