;; 1. $ emacs -q -l test.el    -> note minibuffer font size is bigger
;; 2. M-x test-mode            -> note mode-line background color changes
;; 3. M-x clone-indirect-buffer
;; => Error: "face-attrs--make-indirect-safe: Wrong type argument: listp, test-modeline"


;; This could be in init.el
(add-hook 'minibuffer-setup-hook #'(lambda ()
                                     (face-remap-add-relative 'default :background "#8888cc" :height 2.0)))


;; Example code
(defface test-modeline
  '((t
     :background "#FF8888"))
  "Test face.")

(defvar test--orig-modeline nil)

(defun test--enable ()
  (setq-default test-orig-modeline 'mode-line-active)
  (setf (alist-get 'mode-line-active face-remapping-alist) 'test-modeline)
  (redisplay))

(defun test--disable ()
  (setq-default mode-line-active 'test-orig-modeline)
  (setf (alist-get 'mode-line-active face-remapping-alist) 'test-orig-modeline)
  (redisplay))

(define-minor-mode test-mode
  "Enable Test minor mode."
  :init-value nil
  :global t
  :lighter " Test"
  (if test-mode
      (test--enable)
    (test--disable)))