Hi Markus Berchtold,
The two CSS files convey rules to style the action menus and dialogs in Sitefinity administration respectively. These files are ones included in the combined CSS file which is applied to Page Editor. So you are not missing anything. It looks like they are requested by a control which thinks they are part of the Public theme.
We have logged a bug for this issue. You should not experience any problems because of these two files not being loaded because they are already applied to Page Editor.
the Telerik team
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