CSS Animations: Keyframes vs Transitions
Comparing CSS transitions and @keyframes animations — when to use each and performance considerations.
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Tags: CSS animations vs transitions, CSS animation tutorial, keyframes vs transition
CSS Animations: Keyframes vs Transitions CSS offers two motion mechanisms: for state-change responses, and for self-contained animation sequences. Choosing the right one is mostly about context, not capability. --- How do I use transitions? smooths the change between two property values when something triggers the change — a hover, a class toggle, a focus state. Transitions require an external trigger. When the triggering state reverts (hover ends), the transition plays in reverse automatically. Shorthand for Multiple Properties --- What is Animations: Self-Contained Motion? animations run on their own timeline, independent of element state. They are better for: Loading spinners and progress indicators Entrance animations (fade in, slide up) Looping attention-grabbing effects Complex…
Frequently Asked Questions
What is the difference between CSS transitions and animations?
CSS transitions respond to state changes — they animate between two values when a property changes (like on hover). CSS `@keyframes` animations run independently of state changes and support multiple intermediate steps, looping, and precise timing control. Transitions are for hover/focus responses; animations are for loading spinners, entrance effects, and looping motion.
Which CSS animation approach is better for performance?
Both perform equally well when animating only `transform` and `opacity` — the two compositor-thread properties. The performance difference comes from what you animate, not which mechanism you use. Avoid animating `width`, `height`, `top`, `left`, or `background-color` with either approach, as these trigger layout and paint.
How do I animate opacity with CSS?
For a one-time hover effect, use `transition: opacity 0.2s ease`. For an entrance animation or loop, define `@keyframes fadeIn { from { opacity: 0 } to { opacity: 1 } }` and apply it with `animation: fadeIn 0.3s ease both`. Prefer `@keyframes` for entrance/exit animations where you need the `animation-fill-mode: both` behavior.
What is animation-fill-mode?
`animation-fill-mode` controls element styles before and after the animation plays. `both` applies the first keyframe styles before the animation starts (useful for entrance fades) and retains the last keyframe styles after it ends. Without `fill-mode: forwards` or `both`, the element snaps back to its original styles when the animation completes.
How do I reduce CSS animation jank?
Animate only `transform` and `opacity`. Add `will-change: transform` to animated elements to signal GPU promotion. Avoid triggering animations on layout-affecting properties. Debounce scroll-triggered animations so they don't fire continuously. Test in DevTools Performance tab with CPU throttling enabled to reproduce lower-end device behavior.
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