genjutsu-css-native

CSS Native — Zero-Dependency Animations & Visual Techniques

When to Use CSS Native vs Library

Situation	Decision
< 3 animations on the page	CSS native
Scroll-driven reveal/parallax	CSS native (animation-timeline)
Enter/exit from display: none	CSS native (@starting-style + transition-behavior: allow-discrete)
Tooltip/popover positioning	CSS native (anchor positioning)
Page transitions (MPA or SPA)	CSS native (View Transitions API)
Complex multi-step timeline (5+ tweens)	GSAP
Stagger across dynamic list (unknown count)	GSAP or Framer Motion
Physics-based spring with interruption	Framer Motion
Morph between SVG shapes	GSAP MorphSVG

Rule of thumb: if you can express it in a @keyframes + one animation-timeline, stay in CSS. The moment you need imperative control, sequence coordination, or runtime values — reach for a library.

---

Scroll-Driven Animations

Scroll Progress Timeline

Animate based on scroll position of a container.

.progress-bar {
  animation: grow-width linear both;
  animation-timeline: scroll(root block);
}

@keyframes grow-width {
  from { transform: scaleX(0); }
  to   { transform: scaleX(1); }
}

• scroll(<scroller> <axis>) — scroller: nearest | root | self, axis: block | inline | x | y
• Default: scroll(nearest block)

View Progress Timeline

Animate as an element enters/exits the scrollport.

.reveal {
  animation: fade-in linear both;
  animation-timeline: view();
  animation-range: entry 0% entry 100%;
}

@keyframes fade-in {
  from { opacity: 0; transform: translateY(2rem); }
  to   { opacity: 1; transform: translateY(0); }
}

animation-range

Controls which segment of the timeline drives the animation.

/* Named ranges: cover | contain | entry | exit | entry-crossing | exit-crossing */
animation-range: entry 0% entry 100%;    /* animate during entry only */
animation-range: contain 0% contain 100%; /* animate while fully visible */
animation-range: entry 25% exit 75%;      /* custom start/end */

Use the Scroll-driven Animations tool to visualize ranges interactively.

---

View Transitions API

Same-Document (SPA)

document.startViewTransition(() => {
  // Update the DOM synchronously
  updateContent();
});

/* Control the transition animation */
::view-transition-old(root) {
  animation: fade-out 200ms ease-out;
}
::view-transition-new(root) {
  animation: fade-in 300ms ease-in;
}

/* Named transitions for specific elements */
.hero-image { view-transition-name: hero; }

::view-transition-group(hero) {
  animation-duration: 400ms;
  animation-timing-function: cubic-bezier(0.4, 0, 0.2, 1);
}

Cross-Document (MPA)

/* Both pages need this */
@view-transition { navigation: auto; }

/* Outgoing page */
.card { view-transition-name: card-detail; }

/* Incoming page */
.detail-hero { view-transition-name: card-detail; }

view-transition-class (group styling)

.card { view-transition-class: card; }

::view-transition-group(*.card) {
  animation-duration: 350ms;
  animation-timing-function: var(--ease-spring);
}

---

@starting-style

Native enter animations from display: none — no JS timing hacks.

.dialog {
  opacity: 1;
  transform: translateY(0);
  transition: opacity 300ms ease, transform 300ms ease,
              display 300ms allow-discrete;

  @starting-style {
    opacity: 0;
    transform: translateY(-1rem);
  }
}

.dialog[hidden] {
  opacity: 0;
  transform: translateY(-1rem);
  display: none;
}

Key rules:

• transition-behavior: allow-discrete (or shorthand allow-discrete in the transition) enables transitioning display and overlay
• @starting-style block defines the "from" state when the element first renders
• Combine with [popover] and <dialog> for native modals with zero JS animation code

---

Anchor Positioning

CSS-native positioning of tooltips, popovers, and floating UI relative to a trigger.

.trigger {
  anchor-name: --my-trigger;
}

.tooltip {
  position: fixed;
  position-anchor: --my-trigger;
  inset-area: top center;
  margin-bottom: 0.5rem;

  /* Fallback if no space on top */
  position-try-fallbacks: --bottom;
}

@position-try --bottom {
  inset-area: bottom center;
  margin-top: 0.5rem;
}

Combine with @starting-style for animated tooltips:

.tooltip[popover]:popover-open {
  opacity: 1;
  transform: scale(1);
  transition: opacity 150ms ease, transform 150ms ease,
              display 150ms allow-discrete, overlay 150ms allow-discrete;

  @starting-style {
    opacity: 0;
    transform: scale(0.96);
  }
}

---

Container Queries + Contextual Animations

Adapt animations to the component's container size, not the viewport.

.card-container {
  container-type: inline-size;
  container-name: card;
}

@container card (min-width: 400px) {
  .card-content {
    animation: slide-in-right 400ms var(--ease-out-expo);
  }
}

@container card (max-width: 399px) {
  .card-content {
    animation: fade-in 300ms ease;
  }
}

Container-relative units in keyframes:

@keyframes slide-in-right {
  from { transform: translateX(10cqw); opacity: 0; }
  to   { transform: translateX(0); opacity: 1; }
}

---

Advanced Visual Techniques

clip-path Transitions

.reveal {
  clip-path: inset(0 100% 0 0);
  transition: clip-path 600ms cubic-bezier(0.77, 0, 0.175, 1);
}
.reveal.visible {
  clip-path: inset(0 0 0 0);
}

Shape morphing: transition between circle(), ellipse(), polygon(), inset() — as long as the function type and point count match.

backdrop-filter

.glass {
  background: oklch(0.98 0.01 250 / 0.6);
  backdrop-filter: blur(12px) saturate(1.8);
  -webkit-backdrop-filter: blur(12px) saturate(1.8); /* Safari */
}

mix-blend-mode

.overlay-text {
  mix-blend-mode: difference;
  color: white; /* inverts over any background */
}

Mesh Gradients (approximated)

.mesh {
  background:
    radial-gradient(at 20% 30%, oklch(0.7 0.2 310) 0%, transparent 50%),
    radial-gradient(at 80% 60%, oklch(0.6 0.18 250) 0%, transparent 50%),
    radial-gradient(at 50% 80%, oklch(0.75 0.15 170) 0%, transparent 50%),
    oklch(0.15 0.02 280);
}

conic-gradient Effects

.spinner {
  background: conic-gradient(from 0deg, transparent 0%, oklch(0.7 0.15 250) 100%);
  border-radius: 50%;
  mask: radial-gradient(farthest-side, transparent calc(100% - 4px), black calc(100% - 4px));
  animation: spin 1s linear infinite;
}

---

Do Not

BAD	GOOD	Why
transition: all 300ms	transition: opacity 300ms, transform 300ms	all triggers transitions on every property change, causes unexpected animations, and prevents browser optimization
Animate width, height, top, left	Animate transform, opacity, clip-path, filter	Layout-triggering properties force reflow on every frame — composite-only properties run on GPU
Scroll-driven animations without fallback	@supports (animation-timeline: scroll()) { ... }	Firefox only added support in v128+, older Safari versions lack support
@starting-style without transition-behavior	Always pair with allow-discrete for display/overlay	Without it, display: none transitions are skipped entirely
Anchor positioning without position-try-fallbacks	Always define fallback positions	Element clips out of viewport if primary position has no space
animation-fill-mode: forwards on scroll-driven	Use both for scroll-driven animations	forwards can lock the element in its final state even when scrolling back