Hello,

you can create two stylesheets - one to be used when user is logged in and one to be used when user is not logged in. Then you can create copy of 'headhtml' web part from 'General' category and modify this copy to generate link to appropriate stylesheet into head section of page in according to if user is logged in or not. You can check if user is logged in using following code:

if (CMS.CMSHelper.CMSContext.CurrentUser.IsAuthenticated)
{
//user is logged in
}
else
{
//user is not logged in
}

Best Regards,

Martin Dobsicek