Proximity scope is a feature of @scope in CSS. While resolving a selector within an @scope () {} at-rule, selectors with the same specificity will rely on DOM proximity to decide a winner above what would have otherwise been source order. This is a whole new step in the cascade for CSS. It’s a bit niche of a concern, but it actually can make CSS work more intuitively, fixing an issue where an obviously closer class is losing to another class just because of the order they appear in the CSS.