/usr/lib/python3/dist-packages/xstatic/pkg/jquery_ui/data/ui/jquery-ui.css is in python3-xstatic-jquery-ui 1.12.0.1+debian+dfsg3-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/python3/dist-packages/xstatic/pkg/jquery_ui/data/ui/../../../../../../../../share/javascript/jquery-ui/css/smoothness/jquery-ui.css