How to apply custom color scheme for xfce mousepad

Question

How to apply custom style for Mousepad 0.5.10 in Debian 12? I created a copy of classic.xml and modified the content of the copy as you can see below. But if I run Mousepad, then the new color-scheme is not listed within preferences > view > color scheme.

$ ls -l /usr/share/gtksourceview-3.0/styles
total 80
-rw-r--r-- 1 root root 5304 14. Sep 2019  classic.xml
-rw-r--r-- 1 root root 7332 14. Sep 2019  cobalt.xml
-rw-r--r-- 1 root root 8637 14. Sep 2019  kate.xml
-rw-r--r-- 1 root root 5310  8. Apr 19:16 my_classic.xml
-rw-r--r-- 1 root root 6498 14. Sep 2019  oblivion.xml
-rw-r--r-- 1 root root 4340 14. Sep 2019  solarized-dark.xml
-rw-r--r-- 1 root root 4265 14. Sep 2019  solarized-light.xml
-rw-r--r-- 1 root root 3441 14. Sep 2019  styles.rng
-rw-r--r-- 1 root root 6214 14. Sep 2019  tango.xml


$ sudo nano /usr/share/gtksourceview-3.0/styles/my_classic.xml

<style-scheme id="my_classic" _name="My-Classic" version="1.0">
  <author>GtkSourceView team</author>
  <_description>Classic color scheme</_description>
  <style name="current-line-number" background="#008A8C"/>
</style-scheme>

Answer 1

It seems that the Mousepad developers have made a change to use gtksourceview4. Based on info from this post on the Xfce forums, I got Mousepad to pick up styles by putting them into gtksourceview-4 directories rather than gtksourceview-3.0.

I only tried directories 1 and 4 in the following list, but I strongly suspect that all of them would work. If a particular folder isn't there, as was the case for the folder under ~/.local/share on my system, just create it.

1. ~/.local/share/gtksourceview-4/styles/
2. /usr/share/gnome/gtksourceview-4/styles/
3. /usr/local/share/gtksourceview-4/styles/
4. /usr/share/gtksourceview-4/styles/

Important Note: the number in these folder names must be 4 and not 4.0.