Try Emacs and https://ess.r-project.org/, which is in every way better than Rstudio in my opinion. For tons of themes, you can refer to https://emacsthemes.com/ and https://melpa.org/#/?q=theme&sort=downloads&asc=false. More importantly, the ESS package in Emacs allow you to edit R code in an extremely smooth way, once you get used to the keybindings.