The idea: uses CSS to detect accessibility issues.

The author uses different code snippets for it. One ensures the outline of the focus is never clipped. Another makes sure that not expanded content (aria-exanded="false") is not displayed. Another one targets aria-invalid elements. A busy container is not displayed in CSS, etc...

Every time you come up with a style that reflects a state or property of something (open, closed, expanded, collapsed, on, off, checked, disabled, busy, locked, selected, sobbing uncontrollably), do not use a class.

And an argument against utility-classes such as Tailwind: If you use these tools, you still need to know CSS. On top of that, you may need to know the tools’ syntax in order to incorporate any CSS that goes beyond what they offer. If you build these tools, please consider how you can use CSS that promotes and reinforces good and accessible underlying HTML syntax.