[mephitix]

CSS Grid really helped me understand/wrangle z-index and stacking contexts. For example, within a grid you can use grid-row/grid-column to position an overlay over a grid item. The z-index will be scoped to that stacking context.

Modular CSS I think is a huge step forward - I totally agree that global scope is killer. As much as people love to hate on CSS-in-JS, I enjoy using styled-components a lot. I've noticed since using it I've been composing CSS instead of inheriting or overriding styles.