What used to be Vue/JS — now often CSS

• Container queries

  Component responds to its container width, not the viewport.

• :has() and :focus-within

  Parent styling from child state without toggling classes.

• Popover + anchor positioning

  Layered menu tied to a button with anchor-name / position-anchor.

• <details> + discrete transitions

  Animated disclosure with @starting-style / allow-discrete where supported.

• Scroll-driven animations

  Scroll-linked motion via animation-timeline: view().

• Reading progress bar

  Top-of-page scroll indicator with scroll(root block)—no JS.

• View Transitions Hybrid

  Same-document transition with document.startViewTransition.

• View Transitions between pages MPA

  Cross-document transition with @view-transition { navigation: auto; }.

• light-dark() + color-scheme

  System light/dark colors without duplicated media queries.

• oklch + color-mix()

  Perceptual colors and variants from one token.

• clamp() fluid type

  Fluid typography without resize listeners.

• progress() interpolation

  Map 100vw between two lengths to a bar width (with @supports fallback).

• Custom Highlight API Hybrid

  Search highlights with ::highlight() + minimal JS.

• @layer

  Ordered cascade slices for design systems.