No page style appearing on Permissions page.
I recommend you to do the following:


delete css files under /sites/default/files/css and then checkout the administrator pages 
go to /admin/appearance and select an administrator them at the bottom of the page. If its already been selected try to use another administrator theme
make sure "Use the administration theme when editing or creating content" is checked
clear your cache using drupal clear cache button under /admin/config/development/performance
Checkout Administer themes permission in the permission page /admin/people/permissions
try to open your site with another browser