Cannot use quickstart-desk-javascript

I wanted to use quickstart-desk-javascript(https://github.com/sendbird/quickstart-desk-javascript)

But after completing all steps written in above readme, I had one problem.
I counldn’t log in “Desk Widget Sample Page”(Please look at below picture)
There is no button to log in below the arrow.

However in source code of this sample page, the button seems to exist.

Do you see what’s wrong?

Thank you.