CSS keyframe animations let you describe how an element’s styles change over time. Define the stages in a named @keyframes rule, then connect that name to an element with animation properties such as duration, timing, and repetition.
How CSS keyframe animations work
A keyframe animation has two parts: a named sequence of style states and an animation configuration applied to an element. The animation-name property connects the element to the matching @keyframes rule. The browser interpolates between keyframes for properties that support interpolation.
Keyframe percentages mark positions along the animation timeline, not seconds. A 50% keyframe is halfway through the animation’s active duration. A single keyframe can specify several properties.
How to create a CSS keyframe animation
- Choose the element and effect. Add a class to the element you want to animate.
- Write a named
@keyframesrule. Define the starting and ending styles, plus intermediate percentages when the effect needs waypoints. - Apply the animation. Set the animation name and the timing options that suit the effect.
.card {
animation: 600ms ease-out 1 both enter;
}
@keyframes enter {
from {
opacity: 0;
transform: translateY(0.75rem);
}
to {
opacity: 1;
transform: translateY(0);
}
}Here, enter is the connection between the rule and the element. The duration is 600 milliseconds, the timing function is ease-out, the animation runs once, and both applies its animated styles before and after the active run as specified by the fill mode.
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from, to, and percentage keyframes
from is an alias for 0%; to is an alias for 100%. Use percentages when the animation needs intermediate states. For example, a three-stage animation can use 0%, 50%, and 100% to describe its start, midpoint, and finish. Keyframe selectors may appear in any order in the stylesheet; the browser uses their positions on the timeline.
If the rule omits its start or end keyframe, the element’s computed style supplies that endpoint. This is useful when an animation should begin from the element’s current style and return to its original state, but it can also produce a different result than an explicitly specified start or finish.
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Properties in keyframes
You can set multiple properties in one keyframe. If a property is omitted at a particular keyframe, it may still interpolate across the animation when possible. A property that cannot be animated in keyframes is ignored for that animation; supported properties in the same rule can still animate. Check that the specific property’s values interpolate as intended rather than assuming every CSS property will produce a smooth change.
Choose animation settings deliberately
The longhand animation properties make each part of the behavior explicit:
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animation-nameselects the named@keyframesrule.animation-durationsets the active run’s length. Its default is0s; if you omit the duration, the animation may produce no visible change even though animation events can still occur.animation-timing-functioncontrols the pace of change between keyframes.animation-delaypostpones the start.animation-iteration-countcontrols how many times the sequence runs.animation-directioncontrols whether repetitions run forward, backward, or alternate direction.animation-fill-modedetermines whether animation styles apply before the run begins or after it ends. Use it when the element needs to retain an animated state outside the active run.animation-play-statecontrols whether the animation is running or paused.
The shorthand can combine these settings, but make sure it includes a nonzero duration when a visible animation is intended. When reading or editing a shorthand, keep the values easy to map to the named sequence; longhands are clearer when a configuration becomes difficult to scan.
Several animations on one element
Apply multiple animations by separating their values with commas. Keep each animation’s configuration aligned with its corresponding name so the relationship remains understandable when the declaration is maintained later.
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Avoid duplicate keyframe names
Duplicate @keyframes rules with the same name do not merge. The last matching rule encountered is used, so accidental duplicate names can silently replace an earlier sequence. Give each sequence a distinctive name and search the stylesheet or build output if an animation unexpectedly uses the wrong stages.
Keyframes or a transition?
Use keyframes when the effect needs intermediate waypoints or control over repetition and direction. A transition is often a more direct fit for a simple change between states. In either case, confirm that the property interpolates as intended, provide an appropriate reduced-motion experience, and evaluate rendering cost in the actual interface.
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Support reduced-motion preferences
Some motion, especially blinking or flashing, can be problematic for people with vestibular disorders, epilepsy, migraine, or other sensitivities. The prefers-reduced-motion media query lets a site provide fewer animations and transitions to people whose operating system is set to reduce motion. For nonessential motion, a straightforward starting point is:
@media (prefers-reduced-motion: reduce) {
.card {
animation: none;
}
}Consider whether a static state preserves the information and function conveyed by the animation. A reduced-motion preference does not automatically mean every animation must disappear: motion that is essential to functionality or information may need a carefully considered alternative. Where appropriate, provide a way to pause or disable animation as well.
Consider performance in the target interface
CSS animations are not automatically inexpensive. The cost depends on the animated properties and the work the browser must perform. Animating box-model properties can trigger layout reflow and repaints; transform can be a useful alternative for some effects, but it is not a universal performance guarantee. Profile the page on the devices and in the conditions that matter for the interface rather than assuming a property or animation will always be smooth.
Troubleshoot common animation problems
- Nothing visibly moves: Check that the element’s
animation-nameexactly matches a defined@keyframesname, and that the duration is greater than0s. - The element jumps to an unexpected state: Check for omitted start or end keyframes, which use computed styles, and verify that the intended properties and values are present at the relevant keyframes.
- An earlier animation definition seems ignored: Look for duplicate rules with the same keyframe name. The last matching rule is used rather than merging the rules.
- One property does not animate: Confirm that the property can be animated in keyframes and that its values interpolate as intended. Other supported properties in the same animation may still work.
- The animation feels sluggish or causes jank: Review whether it animates box-model properties that cause layout or repaint work. Consider whether a transform-based effect fits, then profile the real page and target devices.
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