The website seems to have a bug with syntax highlighting. Pieces of code included in the post text are black, you can still see the actual text if you select it with your mouse. Same bug on Chrome desktop and on Safari on iPad
This is the classic example of why you should always set the foreground color when changing the background color. Otherwise you end up with <code> blocks that are black-on-black. It probably works fine if your browser is in dark mode.
A workaround is to open one of the code elements in the browser's debugger and add color: white to the :not(pre) > code style.
Now, it looks fine to me too. I tested it in Chrome,Firefox, Safari on macOS and on Safari on an iPad yesterday when I wrote my comment and in all cases there were black lines all over the the place. The author corrected the problem, see https://news.ycombinator.com/item?id=48855382