/usr/share/kde4/apps/plasma/packages/org.kde.active.aboutapp/contents/data/style.css is in plasma-active-data 2.0+git2012021101-0ubuntu4~ppa3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | body {
background: url(../images/background.png);
padding: 1em;
}
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