css

Container queries (@container) let you style elements based on the size of their parent container rather than the viewport. This enables truly reusable components that adapt to wherever they're placed, unlike media queries which only respond to the browser window size.

Cascade layers (@layer) let you group CSS rules into named layers with explicit priority ordering. Rules in later-declared layers override earlier ones regardless of selector specificity, giving you architectural control over which styles win without resorting to !important or specificity hacks.

Key CSS performance techniques: minimize render-blocking CSS with critical CSS inlining, use content-visibility for off-screen elements, only animate transform/opacity (GPU-accelerated), avoid expensive selectors, use will-change sparingly, leverage CSS containment, and reduce unused CSS with purging tools.