a small suggestion: in the current Rstudio version, the css corresponding to the different themes seem to be located in:
in the installation folder (in Windows - don't know about linux or mac). However, it is not possible to (easily) understand which css corresponds to which theme, since the the names of the themes are "obfuscated". For example,
A83503B82AD5F306AC7145CA4390FA5D.cache.css - is (I think...) an editor theme, but which one?
Would you consider naming the css files according to the themes they correspond to, so that interested users can more easily "tweak" the default themes to their liking ? Ideally, it would be nice also to be able to save a customized theme to a different file and have the possibility to add it to the RStudio list, but just being able to more easily modify a bit a default one would be a nice feature, IMO.