How to center horizontally the contents of the open file in vim?

Exist several plugins that allow you to get that look, most of them seem to be inspired by Writeroom editor for MacOS.

See for example this screenshot of the the VimRoom plugin, or just search the web for "vim writeroom plugin".

I think you could reach the point using screen. you can open three different windows tiled vertically with

CTRL+a , SHIFT+|

then move to the second one.

Vim isn't meant to be a single, centered document editor (when programming, you want to fill every single pixel with relevant information), so there are only workarounds:

a) You can achieve a larger left margin by expanding the fold column. Unfortunately, this is limited to 12 character cells:

:let &foldcolumn = (&columns - &textwidth) / 2

b) You can create an empty padding window to the left (and potentially also to the right, for symmetry).

:execute 'topleft' ((&columns - &textwidth) / 2 - 1) . 'vsplit _paddding_' | wincmd p

The annoying window split can be cleared with:

:hi VertSplit guifg=bg guibg=NONE gui=NONE