exit app without logout error

 Hello,
I have implemeted login/logout functionalities in my app.
The problems im facing is when the user closes the app by closing the browser instead of the logout button:
 - closing the browser doesn't logout the user automatically. is there a way to solve this?
- if the user goes back to the site before his/her session ends, it bypasses the login process show my first page with CSS not working. and any postback will give me this error  : The resource cannot be found. Description: HTTP 404. The resource you are looking for (or one of its dependencies) could have been removed, had its name changed, or is temporarily unavailable.  Please review the following URL and make sure that it is spelled correctly.
 
any suggestion will be much appreciated

 
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