mjhjmtu

I'm running live knoppix 7.7.1 on a USB stick with persistence.

Metacity has stopped running at bootup, after I did the following. I addded the
file gtk.css to the pre-existing empty directories
/home/knoppix/.config/gtk-2.0/ and /home/knoppix/.config/gtk-3.0/. (See Full
Details for details.)

But after I did that, Metacity no longer runs after the boot. The consequence
is (amongst other things) that windows no longer have a title bar. So to try and
get Metacity to run at bootup again, I deleted gtk.css from both those
directories. But Metacity still doesn't run at bootup.

So I have to set Metacity running manually (e.g., from a terminal).

My questions:

WHY has putting gtk.css into those directories stopped Metacity running at
bootup?

How do I restore the situation so that Metacity runs at bootup, exactly as it
did before?

I realise that a work-around would be to run Metacity from a startup file, But I
want to restore things to how they were before, i.e., Metacity running at
bootup.

Full Details

1. 
   

   The reason for adding the gtk.css file
   to /home/knoppix/.config/gtk-2.0/ and /home/knoppix/.config/gtk-3.0
   is that I want to change the colour of the title
   bar in all windows. And the thread What files to edit to change title bar and border width of Ubuntu 18.04 LTS
   says that putting gtk.css into ~/.config/gtk-3.0/ will achieve this. 
   The contents of my gtk.css are

   
   
   

   .titlebar 
    background: #0759EB;
   
   
   .titlebar:backdrop 
    background: #8A0829;
    color:white;
   
   

   
   

Putting gtk.css in ~/.config/gtk-3.0/ didn't change the colour of the Title bar,
so I added the same gtk.css to ~/.config/gtk-2.0/ as well. But that hasn't
changed the colour of the Title bar either.