It’s in-line, in the HTML source (not an external CSS file). I modified it using dev tools / inspector on Google Chrome for testing purposes - it’s only a temporary change, as soon as the page refreshes it changes back.
So this change would need an update to Manager itself.
Currently I don’t find audit trail that useful. It shows limited information of activity. I’d like to make it so you can drill down into each activity and see what exactly has been changed and possibly revert it too (if desirable).