/usr/share/themes
system themes directory
View muffin themes
muffin-theme-viewer [THEMENAME]
muffin-theme-viewer allows you to preview any installed Muffin theme.
When designing a new Muffin theme, you can use muffin-theme-viewer to measure the performance of a window frame option, and to preview the option.
Name of the theme to be shown (Atlanta by default). It is case-sensitive.
/usr/share/themes
system themes directory
/usr/share/themes/*/muffin-1/muffin-theme-1.xml
theme specification file
Unchanged in 4 releases since Debian 8 (Jessie).