How to set a virtual background as default on the Jitsi meet video conference?

Hello everyone,

I’m using Jitsi as self-hosted and the iframe API for my project. I’m trying to set a plain virtual background as default for the video conferences like the following screenshot.

I have added a background image to the /usr/share/jitsi-meet/images directory and I’m trying to add a custom css to the /usr/share/jitsi-meet/css directory however, I couldn’t realize which element has changed when I set a virtual background. Could you please help me about that?