gistfile1.txt

  (defun center-window (window) ""
         (let* ((current-extension (file-name-extension (or (buffer-file-name) "foo.unknown")))
                (filename (buffer-file-name (current-buffer)))
                (max-text-width 80)
                (margin (max 0 (/ (- (window-width window) max-text-width) 2))))
           (if (and (not (string-match-p (expand-file-name org-roam-directory) (format "%s" filename)))
                    (not (string= current-extension "org")))
               ;; Do nothing if this isn't an .md or .txt file.
               ()
             (set-window-margins window margin margin))))

  ;; Adjust margins of all windows.
  (defun center-windows () ""
         (walk-windows (lambda (window) (center-window window)) nil 1))

  ;; Listen to window changes.
  (add-hook 'window-configuration-change-hook 'center-windows)