It’s great to see that the RStudio theme selection is growing thanks to custom themes being created by users. Many of them are ports of themes that work well in other code editors.
I am (kind of) regularly updating the RStudio Theme Collection which I had first created in August. In the most recent update at the end of October / beginning of November, I have added the following dark themes: Asher, Fairyfloss, Fairyfloss Dark, Mojave Dark, Nord One (a mashup of the Nord theme and Atom’s dark theme), One Dark.
If something is missing on this list or if you have recently created your own RStudio theme, please feel free to create a pull request or open an issue (or simply send me an e-mail).