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.

```css
.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.

```css
.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.

```css
/* 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](https://scroll-driven-animations.style/tools/view-timeline/ranges/) to visualize ranges interactively.

---

## View Transitions API

### Same-Document (SPA)

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

```css
/* 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)

```css
/* 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)

```css
.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.

```css
.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.

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

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

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

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

Combine with `@starting-style` for animated tooltips:

```css
.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.

```css
.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:

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

---

## Advanced Visual Techniques

### clip-path Transitions

```css
.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

```css
.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

```css
.overlay-t