/usr/share/ntop/html/jquery-ui-1.8.16.custom.css is in ntop-data 3:5.0.1+dfsg1-2.2ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/ntop/html/../../javascript/jquery-ui/css/smoothness/jquery-ui-1.10.1.custom.css