This is a Firefox extension that injects some JS to Adobe Connect HTML5 client and enables dark theme.
To install Chromium version (for Chromium, Chrome, new Edge, Brave etc.) you should clone this repository or download source code archive from releases page. Then you can go to chrome extensions page, enable developer mode and choose Load Unpacked and select folder with extension source code inside it and install the extension.
You have to follow this procedure because google wants $5 from me and I don't enjoy paying them. Feel free to pay them and submit extension with your name in Chrome Web Store :)
Download extension from releases page and open it with firefox.
Just join your meeting, press refresh in the extension popup, and enjoy the comfort of dark theme.
Refresh the page to disable dark theme.