Onboard Customisation SVG restrictions

Hello,

I am customizing the layout and theme of onboard trying to have my own keyboard. I am facing troubles while inserting SVG without transparent background while SVG with transparent backgrounds work correctly. The SVG with a background are displayed as an entire white image.

Is there any limitations regarding the background of SVG files? Is it mandatory to have a transparent one?

I am using onboard 1.4.1-2ubuntu1.

Thanks in advance for your feedback.