I opened issue #13894 on the GitHub repo but it was precipitously closed without asking for further details to the user to make sure it is not a real bug (that to me does not seem very professional, but anyway).
The documentation makes you use first the “hugo server” command and with that on localhost I can see the correct webpage with the style provided by the “ananke” theme.
At the end it makes you use the simpler “hugo” command to create the deployable directory with the HTML and CSS code.
Upon opening the main page with a browser the page does not show the styling CSS anymore.
There is no indication in the documentation that this should be the case.
please see the (closed) issue for a screenshot and a zip file of the output directory that I generated from the QuickStart tutorial.