Why does a website look different or have no background for the agent during a Cobrowse session?
If the end-user is behind a login page or the webiste is internal and the CSS and formatting for that page is also behind the login or it is not public or available for the agent, when the agent renders the page and attempts to access the CSS files, since they are not logged in, the website will not render properly missing the formatting of the background.
This is the standard intended functionality.
The resolution to this is to open up the CSS files and make them public facing. This way when the agent renders the page the CSS files will be accessible.