As you suggested, I agree the new grid-line syntax is still lacking…
Are you familiar with Greg Badros’s Constraint CSS (CCSS) (https://www.cs.washington.edu/research/constraints/web/ccss-uwtr.pdf)? Although ancient in web years, the underlying concepts and it’s Cassowary Constraint Solver became the foundation for Apple’s new layout system for Cocoa, Auto Layout. Constraint-based layout primitives offer a much more expressive & intuitive layout paradigm. If you’re curious, I created CSS polyfills for CCSS & Cocoa’s Visual Format Language using Alex Russell’s JavaScript port of the Cassowary solver, check it out:
Also, your book looks great!