It Loop windows at frame, measure and adjust contrast.  Allow to
 set color (face) of background and text by comparing their
 brightness.
This is useful for changing themes during the daytime (circadian
 package) and for highlighting selected window.  Also this works
 for modeline.

Usage:

(add-to-list 'load-path "path_to/selected-window-contrast") ; optional
(when (require 'selected-window-contrast nil 'noerror)
  (setopt selected-window-contrast-bg-selected 0.95)
  (setopt selected-window-contrast-bg-others 0.75)
  (setopt selected-window-contrast-text-selected 0.9)
  (setopt selected-window-contrast-text-others 0.6)
  (add-hook 'buffer-list-update-hook
            #'selected-window-contrast-highlight-selected-window))

How this works:
 1) We get color with `face-attribute' `selected-frame' for
 foreground and backgraound.
 2) Convert color to HSL
 3) adjust brightness in direction of foreground-background average
 4) convert color to RGB, then to HEX
 5) apply color

Customize: M-x customize-group RET selected-window-contrast

Donate:
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Other packages:
- Modern navigation in major modes https://github.com/Anoncheg1/firstly-search
- Search with Chinese	https://github.com/Anoncheg1/pinyin-isearch
- Ediff no 3-th window	https://github.com/Anoncheg1/ediffnw
- Dired history		https://github.com/Anoncheg1/dired-hist
- Copy link to clipboard	https://github.com/Anoncheg1/emacs-org-links
- Solution for "callback hell"	https://github.com/Anoncheg1/emacs-async1
- Restore buffer state	https://github.com/Anoncheg1/emacs-unmodified-buffer1
- outline.el usage		https://github.com/Anoncheg1/emacs-outline-it
- Call LLMs & AIfrom Org-mode block.  https://github.com/Anoncheg1/emacs-oai