External plugin wrapper does not read background-image styles

Hello!

I've been working on a custom theme which needs to apply some styles to XFCE panel. The styles in particular need to apply a background-image to the panel that repeats on the x-axis and stretch to fill on the y-axis.

This works fine for the panel itself, and the internal plugins. The problem is the external plugin wrapper (the subclass of GtkPlug) - it does not read any style properties other than the background-color attribute.

Here is a reference to the source in question: https://gitlab.xfce.org/xfce/xfce4-panel/-/blob/master/wrapper/wrapper-plug.c#L189

As a result, the external plugins are inconsistent with the rest of the panel - notice the colour around the Start button plugin here, which should be the same background as the panel:

I have confirmed via GtkInspector that the wrapper is definitely receiving the background-image attribute, which is what led me to debug further and find the code above.