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+---
+name: hyperframes-css-animations
+description: CSS animation adapter patterns for HyperFrames. Use when authoring CSS keyframes, animation-delay based timing, animation-fill-mode, animation-play-state, or CSS-only motion that HyperFrames must seek deterministically during preview and rendering.
+---
+
+# CSS Animations for HyperFrames
+
+HyperFrames can seek CSS keyframe animations through its `css` runtime adapter. Use this for simple repeated motifs, background motion, shimmer, glow, masks, and non-sequenced decoration.
+
+For scene choreography, GSAP is usually clearer. CSS animations work best when the motion belongs to one element and has a fixed duration.
+
+## Contract
+
+- Put the animated element in the DOM before runtime initialization finishes.
+- Give timed elements a `data-start` value so local animation time matches the clip.
+- Use finite `animation-duration` and `animation-iteration-count` because the negative-delay fallback cannot represent unbounded duration in environments without WAAPI-backed CSS animations.
+- Prefer `animation-fill-mode: both` so seeked states hold before and after active motion.
+- Avoid wall-clock JavaScript, hover-triggered state, and class toggles that depend on user events.
+
+The adapter discovers elements with computed `animation-name`, seeks their browser `Animation` handles when available, and falls back to pausing with negative `animation-delay`.
+
+## Basic Pattern
+
+```html
+<div
+  id="pulse-ring"
+  class="clip pulse-ring"
+  data-start="0"
+  data-duration="4"
+  data-track-index="2"
+></div>
+
+<style>
+  .pulse-ring {
+    width: 280px;
+    height: 280px;
+    border: 4px solid rgba(255, 255, 255, 0.7);
+    border-radius: 50%;
+    animation-name: pulse-ring;
+    animation-duration: 1200ms;
+    animation-timing-function: cubic-bezier(0.2, 0, 0, 1);
+    animation-iteration-count: 3;
+    animation-fill-mode: both;
+  }
+
+  @keyframes pulse-ring {
+    from {
+      opacity: 0;
+      transform: scale(0.82);
+    }
+    35% {
+      opacity: 1;
+    }
+    to {
+      opacity: 0;
+      transform: scale(1.18);
+    }
+  }
+</style>
+```
+
+## Stagger Pattern
+
+Use CSS custom properties to avoid duplicating keyframes:
+
+```html
+<div class="clip dots" data-start="1" data-duration="3" data-track-index="3">
+  <span style="--i: 0"></span>
+  <span style="--i: 1"></span>
+  <span style="--i: 2"></span>
+</div>
+
+<style>
+  .dots span {
+    display: inline-block;
+    width: 18px;
+    height: 18px;
+    margin-right: 10px;
+    border-radius: 50%;
+    background: currentColor;
+    animation: dot-pop 900ms ease-out both;
+    animation-delay: calc(var(--i) * 120ms);
+  }
+
+  @keyframes dot-pop {
+    from {
+      opacity: 0;
+      transform: translateY(18px) scale(0.75);
+    }
+    to {
+      opacity: 1;
+      transform: translateY(0) scale(1);
+    }
+  }
+</style>
+```
+
+## Good Uses
+
+- Decorative loops with a known repeat count.
+- Mask, glow, shimmer, grain, and subtle parallax layers.
+- Simple one-element entrances where a full JS timeline would be excessive.
+
+## Avoid
+
+- Infinite CSS animations unless you have verified the browser exposes seekable WAAPI-backed CSS animation handles. Prefer a finite iteration count covering the visible duration. If you do use `infinite`, add `data-duration` to the root element — see Composition Duration below.
+- Animating layout properties like `top`, `left`, `width`, or `height` when transforms work.
+- Relying on hover, focus, scroll, or media queries to trigger render-critical motion.
+- Changing animation classes after startup unless another deterministic timeline controls that change.
+
+## Composition Duration
+
+The render engine needs to know the composition's total length. GSAP timelines report this automatically; CSS-only compositions have no timeline object, so the runtime infers duration from the longest running animation's computed end time (`animation-delay` + `animation-duration` × finite `animation-iteration-count`, per element with `data-start` added as an offset). `data-duration` on the root element is optional whenever every CSS animation on the page is finite — you don't need to add it just because the composition is CSS-driven.
+
+`animation-iteration-count: infinite` (or any unresolved/unbounded animation) has no finite end time, so it cannot be auto-inferred. If the composition's only animation is infinite, you **must** add `data-duration="<seconds>"` to the root `[data-composition-id]` element with your intended total length — `npx hyperframes lint` errors on this case (`root_composition_missing_duration_source`) precisely because there is nothing for the runtime to infer.
+
+```html
+<div
+  data-composition-id="root"
+  data-start="0"
+  data-duration="6"
+  data-width="1920"
+  data-height="1080"
+>
+  <div class="clip spinner" data-start="0" style="animation: spin 1s linear infinite"></div>
+</div>
+```
+
+## Validation
+
+After editing CSS animation compositions:
+
+```bash
+npx hyperframes lint
+npx hyperframes check
+```
+
+## Credits And References
+
+- HyperFrames adapter source: `packages/core/src/runtime/adapters/css.ts`.
+- Duration auto-inference: `packages/core/src/runtime/init.ts` (`resolveAdapterDurationFloorSeconds`), `getInferredDurationSeconds` in the adapter above.
+- MDN CSS animation documentation: https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Properties/animation
+- MDN `animation-fill-mode`: https://developer.mozilla.org/en-US/docs/Web/CSS/animation-fill-mode