fluidlan vim colorscheme is a modified version of space-vim-dark, which is in turn derived from spacemacs-dark-theme. The main differentiator from spacemacs-vim-dark is the lack of orange, except for TODOs and FIXMEs. This theme is somewhat closer to the original spacemacs dark theme.
Follow your favourite plugin manager's instruction, e.g., vim-plug:
Plug 'jhwheeler/fluidlan-vim'colorscheme fluidlan
set termguicolors
hi Normal ctermbg=NONE guibg=NONE
hi LineNr ctermbg=NONE guibg=NONE
hi SignColumn ctermbg=NONE guibg=NONE