/usr/share/python-djangocms-admin-style-common/sass/mixins/_all.scss is in python-djangocms-admin-style-common 1.2.2+dfsg-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | @import "_custom.scss";
@import "_zindex.scss";
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