One of the concepts I share in the book is on the idea of viewing HTML as a relational structure. Like a database. And how viewing it in that way helps you to better understand positioning (even with CSS). Because re-framing it in this way automatically gets you thinking about your elements, and the CSS that binds them, more holistically.
The most common way that people trip themselves up when working with HTML and CSS is by becoming myopic with regard to the specific section or element they're dealing with, and not seeing the whole forest so to speak. Making them unable to see why a problem in their CSS is happening.
Or to know what they need to do to create a certain thing in their layout.
A lack of a holistic understanding (how elements relate to other elements, and how CSS fits into this), and thereby view is what causes this.
My two latest articles goes into more detail re this: