/usr/share/themes/NumixBlue/index.theme is in numix-blue-gtk-theme 0.54.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 | [Desktop Entry]
Type=X-GNOME-Metatheme
Name=Numix Blue
Comment=Variant of Numix with blue highlights
Encoding=UTF-8
[X-GNOME-Metatheme]
GtkTheme=NumixBlue
MetacityTheme=NumixBlue
IconTheme=Adwaita
CursorTheme=Adwaita
ButtonLayout=:minimize,maximize,close
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