I can see whole lines and select the text in a desktop Firefox, but the fonts are messed up (thinned and otherwise tweaked) and colors are set to reduce the contrast, making it hard to read. As with most of the design-related articles, I had to use the reader mode to actually read it. But the content can be guessed from the title (with a hint that it is about CSS) anyway: they have simply removed CSS class selectors, replacing them with element selectors, adding combinator selectors, pseudo-class selectors, and so on.