I Am Also Facing The Same Issue.

Solution:

Delete The Browsing Data From Your Device (Clear Your Cache).

The Above Trick Is Working For Me!!

HI,
The offline page appears when the system lost connection to the server, here in this case the odoo service may be down for some reasons and thus you get this message.

When ever you see this page, check the status of odoo service and see logs for more information.

Thanks

Check the url you have input in the browser. Also check the port number on which the service is running. If this does not help try inputting the -p flag with your desired port number in execution script.