Problem: The other day I had a problem with CSS in my app. I had installed a SharePoint hosted app on a team site. Everything was properly set up, the app environment, the app url, but still the app was not working as expected. The home page opened properly but css was not loaded and all other links were not working.
Solution: Finally after searching a lot I figured out the issue. The issue was that the web application in which the app was installed didn’t have a root site collection(/). After creating the root site collection the app started working properly.