Improve private content visualization
Current private content visualization is very detrimental for the users who are able to see it. It has a very intrusive diagonal hachure and also a transparency effect.
You can view it by creating a private content in your own profile.
We should add something informing the user that the content is private, but needs to be something more subtle. An idea is to add an icon (like a ui-icon-locked from https://api.jqueryui.com/theming/icons/) somewhere in the content header with a comprehensive title ("This is a private content").