/usr/share/themes/Radiant-MATE/index.theme is in ubuntu-mate-themes 18.04.11.
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 13 | [Desktop Entry]
Type=X-GNOME-Metatheme
Name=Radiant-MATE
Comment=Radiant-MATE theme
Encoding=UTF-8
[X-GNOME-Metatheme]
GtkTheme=Radiant-MATE
MetacityTheme=Radiant-MATE
IconTheme=Radiant-MATE
CursorTheme=mate
CursorSize=24
ButtonLayout=menu:minimize,maximize,close
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