bug#50141: Current part of emacs red, other parts blue

[Eli Zaretskii]

> From: 積丹尼 Dan Jacobson
>  <jidanni@jidanni.org>
> Date: Sat, 21 Aug 2021 14:05:45 +0800
> 
> $ emacs
> C-x 2
> C-x 3
> C-x 2
> C-x 3
> We have chopped the screen into little chunks.
> It would be nice to have the current chunk's background e.g., red,
> and the other chunks' blue.
> https://stackoverflow.com/questions/33195122/highlight-current-active-window
> didn't work for me.

Emacs's way to mark the current window is by changing the way the mode
line is displayed.