Publish.css gets overwritten after a few minutes on Obsidian Publish

What I’m trying to do

Use the royal velvet theme css as the css for Obsidian Publish.

Things I have tried

Copy paste the css and rename it. Delete and reads the css.

what happens

The css shows changes on my published site, then promptly disappears after a few minutes and reverts to the original theme. Don’t know what’s happening for it to be overwritten like this as it’s happening if its own accord.