They're not that complex if you understand CSS

And let's face it… to understand the example code you only need understand what > + * do in CSS

Using intrinsic sizing, and the sorts of approaches Andy Bell suggests reduces the volume of CSS enormously and can often get rid of media queries and huge numbers of selectors that get repeated across viewport sizes

I'd really encourage you to watch this talk by Andy https://www.youtube.com/watch?v=5uhIiI9Ld5M