GTK interface modification

[DJ Stauffer]

Hello.

There is a modification I would like to make to Emacs' GTK interface.  I 
have tried a number of solutions to give myself a visual cue as to which 
window in a frame is selected, including changing the color of the 
non-selected windows' backgrounds, changes to the powerline colors, 
etc.  However, I have not found any of this solutions to be 
satisfactory, and occasionally I will still start typing text intended 
for one window when a different window is actually selected.

What I'd like to do is put a one or two pixel border (of whatever color 
I configure, naturally) around the outer edge of the window, to indicate 
that the window is selected.

I have also tried just changing the background color of the fringes, but 
I was unhappy with the results of that also, and would really prefer a 
border around the whole outer edge of the window.

So, I'm looking for suggestions as to where to start.  I realize the C 
code, in particular, the display code is far from simple, but I am 
willing to give it a try.  If anyone has any pointers/recommendations on 
how to accomplish this, I would very much appreciate it.

DJ