ZenithOS was (RIP, long live ) a fork of TempleOS.
The default theme for ZenithOS was so great that I decided to port it to Neovim.
Use your favorite package manager to install that theme. It requires Lush.nvim to be working, so make sure to install it too.
For packer.nvim just install it like that :
use { 'L0Wigh/zenith.nvim', requires = {'rktjmp/lush.nvim'} }- gitsigns