Simple Dark is a colorscheme aimed at being easy to read and focus with. The goal is to write with as few distractions as possible!
If you're using something like vim plug you can simply add
Plugin 'tek256/simple-dark'
and run :PlugInstall to make sure the scheme is downloaded.
otherwise you can just copy the colors folder to your vim colors folder (usually ~/.vim/colors/).
git clone https://github.com/tek256/simple-dark/ ~/.vim/colors/simple-dark/
Once you have the scheme just adding either of the variants as colorscheme looks like
colorscheme simple-dark
or
colorscheme simple-dark-transparent
Generally most other terminal emulators / editors have a dedicated "themes" folder. Each of the respective config files has a comment at the top of the file contents to give hints as to where to put the file!
Copy the contents of the respective files into your own config files. The config files in this repository only set colors, and do not assume any other non-apperance configurations.