Files within the views
folder cannot be loaded. They will throw a 404 error due to the httpHandler
configured in the Web.config
there. This is for security, as you do not want your .cshtml files publicly accessible.
<httpHandlers>
<add path="*" verb="*" type="System.Web.HttpNotFoundHandler"/>
</httpHandlers>
Include the css file from any other folder and you should be fine.