advanced / power-user theming options (CSS)

Allow manual CSS input for theming, perhaps hidden under an "advanced" toggle button (Chrome settings style).

This would allow those of us who can CSS to quickly style the tree to our liking, and perhaps provide a way to experiment for an upcoming updated UI and (perhaps, as a bonus, not my request), themes.

I absolutely love this addon (so much that I paid for it right away, not even sure I need the "paid" features), and really the only thing I see ATM to make it great is a prettier theme (I, for one, would go with something much more barebones / minimalistic and that would fit better with Chrome's UI).

Update: I have found out about Devtool's "Local Overrides" feature (has to be enabled in settings) allows persisting of edits under a local folder  - meaning it's also possible to sync the edits between multiple machines, so there's no need to wait for those that want to start tweaking the UI right away.