I guess render-blocking isn't really a thing, the HTML spec only describes script-blocking and is light on the rendering aspects. Now most web pages have styles

I guess render-blocking isn't really a thing, the HTML spec only describes script-blocking and is light on the rendering aspects. Now most web pages have styles and scripts and since styles block scripts, you usually perceive styles as render-blocking. But this web page doesn't have any scripts, so the browser reaches DOMContentLoaded right after parsing the HTML and does the first paint while the request for the style is still in flight. At least that's my theory. You could test this by inserting an empty <script> tag into the <body>, which should delay DOMContentLoaded until the style arrives and prevent the flash of unstyled content.